fails to resolve planet.gnome.org when forwarding and DNSSEC validation is on

When I have Knot Resolver 5.5.0 on Debian Bullseye set to forward requests, Knot Resolver fails to resolve planet.gnome.org with SERVFAIL.

The problem occurs when forwarding to either Quad9 or Cloudflare, with different systems on different networks (even in different countries). The problem does not happen when I disable forwarding. It also does not happen when I add +cd.

frederik@torino:~$ kdig planet.gnome.org
;; ->>HEADER<<- opcode: QUERY; status: SERVFAIL; id: 51346
;; Flags: qr rd ra; QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0

;; QUESTION SECTION:
;; planet.gnome.org.   		IN	A

;; Received 34 B
;; Time 2022-04-13 17:59:50 CEST
;; From ::1@53(UDP) in 294.8 ms
frederik@torino:~$ kdig +cd planet.gnome.org
;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 3633
;; Flags: qr rd ra cd; QUERY: 1; ANSWER: 4; AUTHORITY: 0; ADDITIONAL: 0

;; QUESTION SECTION:
;; planet.gnome.org.   		IN	A

;; ANSWER SECTION:
planet.gnome.org.   	894	IN	CNAME	router-default.apps.openshift4.gnome.org.
router-default.apps.openshift4.gnome.org. 900	IN	A	8.43.85.5
router-default.apps.openshift4.gnome.org. 900	IN	A	8.43.85.3
router-default.apps.openshift4.gnome.org. 900	IN	A	8.43.85.4

;; Received 127 B
;; Time 2022-04-13 17:59:56 CEST
;; From ::1@53(UDP) in 136.4 ms

Log:

Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][policy][07606.00] request packet:
                                       ;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 7606
                                       ;; Flags: rd  QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0
                                       
                                       ;; QUESTION SECTION
                                       planet.gnome.org.                A
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][policy][07606.00] following rrsets were marked as interesting:
                                       ;; selected from ANSWER sections:
                                       ; ranked rrset to_wire true, rank 060 (secure auth), cached false, qry_uid 1, revalidations 0
                                       planet.gnome.org.           614        CNAME        router-default.apps.openshift4.gnome.org.
                                       ; ranked rrset to_wire true, rank 021 (omit auth), cached false, qry_uid 1, revalidations 0
                                       planet.gnome.org.           614        RRSIG        CNAME 5 3 900 1651937377 1649345377 40692 gnome.org. LwqhAFM+ukN4HHE6QBHSehacwNgodYZrwGykePnayxgD4WCELd887iW7xnQm+CgebWligBJhFLQB5a0VV13j0UD95ji2q+1QBQbJ/lcxdHoh++i2Bhb0nWHQ148FsoE613oMX5wwWm4fpN0fmRPUugKXD2f5fAGFBD83e82QBZk=
                                       ; ranked rrset to_wire false, rank 060 (secure auth), cached false, qry_uid 5, revalidations 0
                                       .                           27913        DNSKEY        256 3 8 AwEAAak/ZU9wDNQD7XTAGTDkn32UR8I6auRDekbGky+yyWKdUHmwAJv90YHCUTib8aVBgNgbxkeeZGRx3W4+XhMZbfUr5fMwmD3u9P2yzJpbRtjGNM/XZvzGs9HHNymz3Bp851anHZfNy6pJud265/XMKzFlAY8sMJjum0hvx/DuCDELLyhsvdfOD9rHM93UXO0bcAjvI8tjZsGI+Pfp9KdxF9vS/sAzpFXKsldix+e6xv8rRS6WPg2LAooxF+eO5DgFSilYmnyCK4VPJ7ntjD/8m0bs128ZT1eY3oXCbojDv59lLAgrdGSbcVxQF2KHoUHDmkOC5BzG/1xRtW4v/3y4/H8=
                                       .                           27913        DNSKEY        257 3 8 AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3+/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kvArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+eoZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfdRUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwNR1AkUTV74bU=
                                       ; ranked rrset to_wire false, rank 021 (omit auth), cached false, qry_uid 5, revalidations 0
                                       .                           27913        RRSIG        DNSKEY 8 0 172800 1651449600 1649635200 20326 . e/e+lsjJGKLiH638XbnFQrI1EUG8CTYh52loAQkKdzX2YzXpTePNDuvPAF7EreJoBNS9EabkwvLwo2O16kXu5kK7TIznS2IO4krC/7ILGVZAbq9EhdsIBKInkBavnokBC+qRrvE78wvbMcl/pt92j5AuoPMmv5lOdowxW/U1m8/MgLh1wU07tkZ2HRGRP6pGMefWDqzb3AvHnEp5rzMnpcOlrVQLPDutztZ6kpRMhTHnL+QN3BqYYIFFg/IQn+YvVSyHR/6/8UTawV9kLSYkab3Cbhgb6jYbxlOG8LcXvtTGwq/PfOcZjttBSsar3X7RjyGYM2hAfrGkMf7gk4X4KA==
                                       ; ranked rrset to_wire false, rank 060 (secure auth), cached false, qry_uid 8, revalidations 0
                                       org.                        35188        DS        26974 8 2 4FEDE294C53F438A158C41D39489CD78A86BEB0D8A0AEAFF14745C0D16E1DE32
                                       ; ranked rrset to_wire false, rank 021 (omit auth), cached false, qry_uid 8, revalidations 0
                                       org.                        35188        RRSIG        DS 8 1 86400 1650906000 1649779200 47671 . gt0yxpNr3DEe3vdglp5pAUwx7Mudxs+wrfsn/UY0a8Qu0hbwygtyxBDGkAbpxlXH0tLGTdcHfselrNekixdXHAnoSHZKiyZNX5OEp3wShJoqln/+0Qs6VLgHrACcoUFQEZnXGTer2flE3imPYux6LPaY+vv2KVGcgJCxkMWgjY/2uMsc03h2XcDplQr6ESdeA7gnxA9pxvjIvY793GTgnybGVbAtgSQSCxvxTClpZxsltuxF+ZBGTxeveNtgLEinTQpQUNy6aekL+H/PEsk6R7S/y8Cx8j6OIdg1MEpTr0Sz6wVJPsD7RhQpAjTbMx2V+2j4is/5815kC4HVKHtg4g==
                                       ; ranked rrset to_wire false, rank 060 (secure auth), cached false, qry_uid 11, revalidations 0
                                       org.                        107        DNSKEY        256 3 8 AwEAAa5uc5s6co7l6C0rgiH0om3XgV6pe2aWmtiNL5/gN82xImSB5ovvjRg1TPfcqNq1CCjtafdWTdtrX2f9hzDMJ1vZxzgcyRDYroiC22kaGQHtlLpw73pVHHrTzqjuJ0lPeko0/SDI0iBIqimY2mT3KJTts3gbXywksWjIHcw5FTAV
                                       org.                        107        DNSKEY        256 3 8 AwEAAbdHIC3iJRkEm4k0aIcj1Q5JPlyCkazmt0j2wFIXze88D5yTStbMFEjVGhTCNVtKGomSxz89GnnCA+MdkDzlJJofSNigEUoTZp5U6tEgtt61NNrKxz0GnJkW/1yeS5dP27hYCSBp9264feY/7z/wjoZyKfbsoymBrC5EZA6iHxFd
                                       org.                        107        DNSKEY        257 3 8 AwEAAexZJ/1wfyNCxNPrTZizaG7UlibGhP+AyogR6bqjptKweEgE4gD8GxRQJkt+Fn5pCoNqzmm1ZnEoKqvm93uOYtbKkYQDGH+W69J66MSKpgIyS+mT/4iaXn+lpb5o99l/sf7lHMa975O/fqN6aPUll4hUbN2T1LHv6HzQuQCtNRJA8jHGwX5q0NMmh2Z+yaG6B9cISerje9l5L+ID2ydJ6zXquYteoIUvX2xzqnXCdHPSvD+oL6R/weW+tztdFS1hok/1z3tn5NzmcaOLll9nXniCozEpLFEGPswyvtphWgCYhI8bBTqhUsIwfIwLSBQTEg2oCX7sS5CbXg44OqwhIW8=
                                       ; ranked rrset to_wire false, rank 021 (omit auth), cached false, qry_uid 11, revalidations 0
                                       org.                        107        RRSIG        DNSKEY 8 1 900 1651332155 1649514155 26974 org. dSvEYdnhQOlzIu9rs3M/kjais/ifG51gF4IKE6GEwikhx/tYFrJuUuGzXpqoQcOkdoZXySoUYoMVF3wwUR7aD8EH+D5NQ4CmGLs1lQil6GGE+CKjglZPZrrklIsVhBmD+AZLAC+HIMkOX7vPLrqPz93IqUs+NtIRY15VEvi15JMSydNUIvmxc1HTPaar6r50TxKwfIR92pYDXWqKTe5HQPJ1uj55oyUAwtEISjKM/BdoV5RRjyC+1+i/by9wkGIJLMCkzX/4UnGqBM2jFm66due25GULAMZRYvnhqQvMMc/yyIe3NoeeMh7wqIXqRaHhXNZfjPXNaCOxkPHVeJuYAg==
                                       ; ranked rrset to_wire false, rank 060 (secure auth), cached false, qry_uid 14, revalidations 0
                                       gnome.org.                  6809        DS        51496 5 2 F676D322A3E9EE31F1078F38256315214078E46A47064CBDEE76E933739CC8C7
                                       ; ranked rrset to_wire false, rank 021 (omit auth), cached false, qry_uid 14, revalidations 0
                                       gnome.org.                  6809        RRSIG        DS 8 2 86400 1651332155 1649514155 10449 org. Fj9K58DnO3WxVDtJKEk1csWU9WgXfrtJ9ZYXIOiPG5KdI5o9WIbrW51DqidP6QVVWGpzvVs8knf0h8AjneROMEBjLehQa+9uZ6bQ/x/DEElp2mW53q43b33I6Rt2rjlbazhjFSt+f9BuWPf3wke4IbRK6/pf57TuGgKYBuVwQwo=
                                       ; ranked rrset to_wire false, rank 060 (secure auth), cached false, qry_uid 17, revalidations 0
                                       gnome.org.                  264        DNSKEY        256 3 5 AwEAAaMI/dz7JwEtjvpr1uCvjs1AvVxiT4dwQGOXzp6r+pQXazhDn6+TlJDh0aEnwFc76ujViKcMruPsS49dtoCAmhBPuI2g+CGyr/PgAfxM4czfak8kKvIdxh1UMQrcIJ/rKJ5eue7fI2BG3plq9oMIPmDEOoPU4ePjIY4M/qrbjcev
                                       gnome.org.                  264        DNSKEY        257 3 5 AwEAAbRD7AymDFuKc2iXta7HXZMleMkUMwjOZTsn4f75ZUp0of8TJdlUDtFtqifEBnFcGJU5r+ZVvkBKQ0qDTTjayL54Nz56XGGoIBj6XxbG8Es+VbZCg0RsetDk5EsxLst0egrvOXga27jbsJ+7Me3D5Xp1bkBnQMrXEXQ9C43QfO2KUWJVljo1Bii3fTfnHSLRUsbRn8Puz+orK71qxs3G9mgGR6rmn91brkpfmHKr3S9Rbxq8iDRWDPiCaWkI7qfASdFk4TLV0gSVlA3OxyW9TCkPZStZ5r/WRW2jhUY/kjHERQd4qX5dHAuYrjJSV99P6FfCFXoJ3ty5s3fl1RZaTo8=
                                       ; ranked rrset to_wire false, rank 021 (omit auth), cached false, qry_uid 17, revalidations 0
                                       gnome.org.                  264        RRSIG        DNSKEY 5 2 900 1651937377 1649345377 40692 gnome.org. FhZSI3iYe2SLfWAJR7DH4bOTTD4AlkPf9OsFZH6nhBJQEk9H8cRkHUzLUczY41daJwDKxlUnnEkEOa1jS8E8EXm3KSSxkraZv6BLsdhxB6UjbYT6ZrhzbneO1sygYc/6IU70DpryKNa6R9jPLEUEphez9MR6Bf/VREtkYNUnVXU=
                                       gnome.org.                  264        RRSIG        DNSKEY 5 2 900 1651937377 1649345377 51496 gnome.org. jgJHprIvEOZL5K6sZhGKrjQEsU368ZzMJ/PJhQpeXz47HwfF0AhTycWSwWG8enqpFhl/QY2n2IEnnTtBC3IytvZBd+SfL82lkuGU1eDaSR4pkMiJCTLEitFEMlRj950A2S1RYxVafJAlJR0MrLEcgUYap+V9OVrGjoSnXTIs9XOY0aj0iTNRT5nm1RC533QKCu5PDwQlXbwUWC0LoYM3oHMG5sbliD0Sy2nObYs9cf7BfkLb97iZiJcQKNm5fpDnG4qaLlw0GRrybbHi1QeIJisC4Isg1gdZ2cPDntPVS8T0m6I5Dcsx1IvDubhucJ8U2SMIkSKIZ1Aidl+MslSTLw==
                                       ;; selected from AUTHORITY sections:
                                       ; ranked rrset to_wire false, rank 060 (secure auth), cached false, qry_uid 20, revalidations 0
                                       gnome.org.                  16        SOA        ns-master.gnome.org. hostmaster.gnome.org. 1649348977 600 900 86400 3600
                                       ; ranked rrset to_wire false, rank 021 (omit auth), cached false, qry_uid 20, revalidations 0
                                       gnome.org.                  16        RRSIG        SOA 5 2 900 1651937377 1649345377 40692 gnome.org. D4nUm9bExjX/lUoG+TgMdYuccR7InE2wSzBLR2a4ocU3IqpNvA7seBmll9x706ImEZ1oxtvXTZbozEG7W1c7KIlo+vvSl4yoQgQl37VncHhfW5U6Q69v9o1XRuledjb7l16OtynblHXQkDmZDrT9vwX0BV6eoZ78QG84lBqpaFk=
                                       ; ranked rrset to_wire false, rank 060 (secure auth), cached false, qry_uid 20, revalidations 0
                                       *.openshift.gnome.org.        2716        NSEC        *.openshift4.gnome.org. A AAAA RRSIG NSEC
                                       ; ranked rrset to_wire false, rank 021 (omit auth), cached false, qry_uid 20, revalidations 0
                                       *.openshift.gnome.org.        2716        RRSIG        NSEC 5 3 3600 1651937377 1649345377 40692 gnome.org. j3xWiApwlF6XY64qJnXepFklLWWOHYpQFl1ZBtEhT0THnbMMgwOUmhzvpCbeWJaNRZiqMNGBLo1g+4gaOA3RpzULFjH8GyW0fuzpZ7qwZAgxUsa9/Ii5tj5rtYTv8zZFkqv9xoQVLfwx09r12Sjrpg/aoXnHs0LEbSkCJWC3lAQ=
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][policy][07606.00] answer packet:
                                       ;; ->>HEADER<<- opcode: QUERY; status: SERVFAIL; id: 7606
                                       ;; Flags: qr rd ra  QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0
                                       
                                       ;; QUESTION SECTION
                                       planet.gnome.org.                A
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.00]   'planet.gnome.org.' type 'A' new uid was assigned .01, parent uid .00
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.01]   => satisfied by exact CNAME: rank 060, new TTL 614
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.01]   <= answer received:
                                       ;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 26361
                                       ;; Flags: qr aa  QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0
                                       
                                       ;; QUESTION SECTION
                                       planet.gnome.org.                A
                                       
                                       ;; ANSWER SECTION
                                       planet.gnome.org.           614        CNAME        router-default.apps.openshift4.gnome.org.
                                       planet.gnome.org.           614        RRSIG        CNAME 5 3 900 1651937377 1649345377 40692 gnome.org. LwqhAFM+ukN4HHE6QBHSehacwNgodYZrwGykePnayxgD4WCELd887iW7xnQm+CgebWligBJhFLQB5a0VV13j0UD95ji2q+1QBQbJ/lcxdHoh++i2Bhb0nWHQ148FsoE613oMX5wwWm4fpN0fmRPUugKXD2f5fAGFBD83e82QBZk=
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.01]   <= rcode: NOERROR
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.01]   <= cname chain, following
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.02]   'router-default.apps.openshift4.gnome.org.' type 'A' new uid was assigned .03, parent uid .00
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.03]   => trying zone: gnome.org., NSEC, hash 0
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.03]   => NSEC sname: range search miss (!covers)
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.03]   => skipping zone: gnome.org., NSEC, hash 0;new TTL -123456789, ret -2
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][plan  ][07606.03]   plan '.' type 'DNSKEY' uid [07606.04]
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.04]     '.' type 'DNSKEY' new uid was assigned .05, parent uid .03
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.05]     => satisfied by exact RRset: rank 060, new TTL 27913
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.05]     <= answer received:
                                       ;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 42892
                                       ;; Flags: qr aa  QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0
                                       
                                       ;; QUESTION SECTION
                                       .                DNSKEY
                                       
                                       ;; ANSWER SECTION
                                       .                           27913        DNSKEY        256 3 8 AwEAAak/ZU9wDNQD7XTAGTDkn32UR8I6auRDekbGky+yyWKdUHmwAJv90YHCUTib8aVBgNgbxkeeZGRx3W4+XhMZbfUr5fMwmD3u9P2yzJpbRtjGNM/XZvzGs9HHNymz3Bp851anHZfNy6pJud265/XMKzFlAY8sMJjum0hvx/DuCDELLyhsvdfOD9rHM93UXO0bcAjvI8tjZsGI+Pfp9KdxF9vS/sAzpFXKsldix+e6xv8rRS6WPg2LAooxF+eO5DgFSilYmnyCK4VPJ7ntjD/8m0bs128ZT1eY3oXCbojDv59lLAgrdGSbcVxQF2KHoUHDmkOC5BzG/1xRtW4v/3y4/H8=
                                       .                           27913        DNSKEY        257 3 8 AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3+/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kvArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+eoZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfdRUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwNR1AkUTV74bU=
                                       .                           27913        RRSIG        DNSKEY 8 0 172800 1651449600 1649635200 20326 . e/e+lsjJGKLiH638XbnFQrI1EUG8CTYh52loAQkKdzX2YzXpTePNDuvPAF7EreJoBNS9EabkwvLwo2O16kXu5kK7TIznS2IO4krC/7ILGVZAbq9EhdsIBKInkBavnokBC+qRrvE78wvbMcl/pt92j5AuoPMmv5lOdowxW/U1m8/MgLh1wU07tkZ2HRGRP6pGMefWDqzb3AvHnEp5rzMnpcOlrVQLPDutztZ6kpRMhTHnL+QN3BqYYIFFg/IQn+YvVSyHR/6/8UTawV9kLSYkab3Cbhgb6jYbxlOG8LcXvtTGwq/PfOcZjttBSsar3X7RjyGYM2hAfrGkMf7gk4X4KA==
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.05]     <= rcode: NOERROR
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.05]     <= parent: updating DNSKEY
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.05]     <= answer valid, OK
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.03]   'router-default.apps.openshift4.gnome.org.' type 'A' new uid was assigned .06, parent uid .00
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][plan  ][07606.06]   plan 'org.' type 'DS' uid [07606.07]
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.07]     'org.' type 'DS' new uid was assigned .08, parent uid .06
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.08]     => satisfied by exact RRset: rank 060, new TTL 35188
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.08]     <= answer received:
                                       ;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 22326
                                       ;; Flags: qr aa  QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0
                                       
                                       ;; QUESTION SECTION
                                       org.                DS
                                       
                                       ;; ANSWER SECTION
                                       org.                        35188        DS        26974 8 2 4FEDE294C53F438A158C41D39489CD78A86BEB0D8A0AEAFF14745C0D16E1DE32
                                       org.                        35188        RRSIG        DS 8 1 86400 1650906000 1649779200 47671 . gt0yxpNr3DEe3vdglp5pAUwx7Mudxs+wrfsn/UY0a8Qu0hbwygtyxBDGkAbpxlXH0tLGTdcHfselrNekixdXHAnoSHZKiyZNX5OEp3wShJoqln/+0Qs6VLgHrACcoUFQEZnXGTer2flE3imPYux6LPaY+vv2KVGcgJCxkMWgjY/2uMsc03h2XcDplQr6ESdeA7gnxA9pxvjIvY793GTgnybGVbAtgSQSCxvxTClpZxsltuxF+ZBGTxeveNtgLEinTQpQUNy6aekL+H/PEsk6R7S/y8Cx8j6OIdg1MEpTr0Sz6wVJPsD7RhQpAjTbMx2V+2j4is/5815kC4HVKHtg4g==
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.08]     <= rcode: NOERROR
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.08]     <= DS: OK
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.08]     <= parent: updating DS
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.08]     <= answer valid, OK
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.06]   'router-default.apps.openshift4.gnome.org.' type 'A' new uid was assigned .09, parent uid .00
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][plan  ][07606.09]   plan 'org.' type 'DNSKEY' uid [07606.10]
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.10]     'org.' type 'DNSKEY' new uid was assigned .11, parent uid .09
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.11]     => satisfied by exact RRset: rank 060, new TTL 107
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.11]     <= answer received:
                                       ;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 52529
                                       ;; Flags: qr aa  QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0
                                       
                                       ;; QUESTION SECTION
                                       org.                DNSKEY
                                       
                                       ;; ANSWER SECTION
                                       org.                        107        DNSKEY        256 3 8 AwEAAa5uc5s6co7l6C0rgiH0om3XgV6pe2aWmtiNL5/gN82xImSB5ovvjRg1TPfcqNq1CCjtafdWTdtrX2f9hzDMJ1vZxzgcyRDYroiC22kaGQHtlLpw73pVHHrTzqjuJ0lPeko0/SDI0iBIqimY2mT3KJTts3gbXywksWjIHcw5FTAV
                                       org.                        107        DNSKEY        256 3 8 AwEAAbdHIC3iJRkEm4k0aIcj1Q5JPlyCkazmt0j2wFIXze88D5yTStbMFEjVGhTCNVtKGomSxz89GnnCA+MdkDzlJJofSNigEUoTZp5U6tEgtt61NNrKxz0GnJkW/1yeS5dP27hYCSBp9264feY/7z/wjoZyKfbsoymBrC5EZA6iHxFd
                                       org.                        107        DNSKEY        257 3 8 AwEAAexZJ/1wfyNCxNPrTZizaG7UlibGhP+AyogR6bqjptKweEgE4gD8GxRQJkt+Fn5pCoNqzmm1ZnEoKqvm93uOYtbKkYQDGH+W69J66MSKpgIyS+mT/4iaXn+lpb5o99l/sf7lHMa975O/fqN6aPUll4hUbN2T1LHv6HzQuQCtNRJA8jHGwX5q0NMmh2Z+yaG6B9cISerje9l5L+ID2ydJ6zXquYteoIUvX2xzqnXCdHPSvD+oL6R/weW+tztdFS1hok/1z3tn5NzmcaOLll9nXniCozEpLFEGPswyvtphWgCYhI8bBTqhUsIwfIwLSBQTEg2oCX7sS5CbXg44OqwhIW8=
                                       org.                        107        RRSIG        DNSKEY 8 1 900 1651332155 1649514155 26974 org. dSvEYdnhQOlzIu9rs3M/kjais/ifG51gF4IKE6GEwikhx/tYFrJuUuGzXpqoQcOkdoZXySoUYoMVF3wwUR7aD8EH+D5NQ4CmGLs1lQil6GGE+CKjglZPZrrklIsVhBmD+AZLAC+HIMkOX7vPLrqPz93IqUs+NtIRY15VEvi15JMSydNUIvmxc1HTPaar6r50TxKwfIR92pYDXWqKTe5HQPJ1uj55oyUAwtEISjKM/BdoV5RRjyC+1+i/by9wkGIJLMCkzX/4UnGqBM2jFm66due25GULAMZRYvnhqQvMMc/yyIe3NoeeMh7wqIXqRaHhXNZfjPXNaCOxkPHVeJuYAg==
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.11]     <= rcode: NOERROR
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.11]     <= parent: updating DNSKEY
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.11]     <= answer valid, OK
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.09]   'router-default.apps.openshift4.gnome.org.' type 'A' new uid was assigned .12, parent uid .00
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][plan  ][07606.12]   plan 'gnome.org.' type 'DS' uid [07606.13]
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.13]     'gnome.org.' type 'DS' new uid was assigned .14, parent uid .12
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.14]     => satisfied by exact RRset: rank 060, new TTL 6809
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.14]     <= answer received:
                                       ;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 8461
                                       ;; Flags: qr aa  QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0
                                       
                                       ;; QUESTION SECTION
                                       gnome.org.                DS
                                       
                                       ;; ANSWER SECTION
                                       gnome.org.                  6809        DS        51496 5 2 F676D322A3E9EE31F1078F38256315214078E46A47064CBDEE76E933739CC8C7
                                       gnome.org.                  6809        RRSIG        DS 8 2 86400 1651332155 1649514155 10449 org. Fj9K58DnO3WxVDtJKEk1csWU9WgXfrtJ9ZYXIOiPG5KdI5o9WIbrW51DqidP6QVVWGpzvVs8knf0h8AjneROMEBjLehQa+9uZ6bQ/x/DEElp2mW53q43b33I6Rt2rjlbazhjFSt+f9BuWPf3wke4IbRK6/pf57TuGgKYBuVwQwo=
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.14]     <= rcode: NOERROR
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.14]     <= DS: OK
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.14]     <= parent: updating DS
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.14]     <= answer valid, OK
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.12]   'router-default.apps.openshift4.gnome.org.' type 'A' new uid was assigned .15, parent uid .00
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][plan  ][07606.15]   plan 'gnome.org.' type 'DNSKEY' uid [07606.16]
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.16]     'gnome.org.' type 'DNSKEY' new uid was assigned .17, parent uid .15
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.17]     => satisfied by exact RRset: rank 060, new TTL 264
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.17]     <= answer received:
                                       ;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 7489
                                       ;; Flags: qr aa  QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0
                                       
                                       ;; QUESTION SECTION
                                       gnome.org.                DNSKEY
                                       
                                       ;; ANSWER SECTION
                                       gnome.org.                  264        DNSKEY        256 3 5 AwEAAaMI/dz7JwEtjvpr1uCvjs1AvVxiT4dwQGOXzp6r+pQXazhDn6+TlJDh0aEnwFc76ujViKcMruPsS49dtoCAmhBPuI2g+CGyr/PgAfxM4czfak8kKvIdxh1UMQrcIJ/rKJ5eue7fI2BG3plq9oMIPmDEOoPU4ePjIY4M/qrbjcev
                                       gnome.org.                  264        DNSKEY        257 3 5 AwEAAbRD7AymDFuKc2iXta7HXZMleMkUMwjOZTsn4f75ZUp0of8TJdlUDtFtqifEBnFcGJU5r+ZVvkBKQ0qDTTjayL54Nz56XGGoIBj6XxbG8Es+VbZCg0RsetDk5EsxLst0egrvOXga27jbsJ+7Me3D5Xp1bkBnQMrXEXQ9C43QfO2KUWJVljo1Bii3fTfnHSLRUsbRn8Puz+orK71qxs3G9mgGR6rmn91brkpfmHKr3S9Rbxq8iDRWDPiCaWkI7qfASdFk4TLV0gSVlA3OxyW9TCkPZStZ5r/WRW2jhUY/kjHERQd4qX5dHAuYrjJSV99P6FfCFXoJ3ty5s3fl1RZaTo8=
                                       gnome.org.                  264        RRSIG        DNSKEY 5 2 900 1651937377 1649345377 40692 gnome.org. FhZSI3iYe2SLfWAJR7DH4bOTTD4AlkPf9OsFZH6nhBJQEk9H8cRkHUzLUczY41daJwDKxlUnnEkEOa1jS8E8EXm3KSSxkraZv6BLsdhxB6UjbYT6ZrhzbneO1sygYc/6IU70DpryKNa6R9jPLEUEphez9MR6Bf/VREtkYNUnVXU=
                                       gnome.org.                  264        RRSIG        DNSKEY 5 2 900 1651937377 1649345377 51496 gnome.org. jgJHprIvEOZL5K6sZhGKrjQEsU368ZzMJ/PJhQpeXz47HwfF0AhTycWSwWG8enqpFhl/QY2n2IEnnTtBC3IytvZBd+SfL82lkuGU1eDaSR4pkMiJCTLEitFEMlRj950A2S1RYxVafJAlJR0MrLEcgUYap+V9OVrGjoSnXTIs9XOY0aj0iTNRT5nm1RC533QKCu5PDwQlXbwUWC0LoYM3oHMG5sbliD0Sy2nObYs9cf7BfkLb97iZiJcQKNm5fpDnG4qaLlw0GRrybbHi1QeIJisC4Isg1gdZ2cPDntPVS8T0m6I5Dcsx1IvDubhucJ8U2SMIkSKIZ1Aidl+MslSTLw==
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.17]     <= rcode: NOERROR
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.17]     <= parent: updating DNSKEY
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.17]     <= answer valid, OK
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.15]   'router-default.apps.openshift4.gnome.org.' type 'A' new uid was assigned .18, parent uid .00
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][plan  ][07606.18]   plan 'openshift4.gnome.org.' type 'DS' uid [07606.19]
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.19]     'openshift4.gnome.org.' type 'DS' new uid was assigned .20, parent uid .18
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.20]     => skipping exact packet: rank 025 (min. 030), new TTL 16
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.20]     => trying zone: gnome.org., NSEC, hash 0
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.20]     => NSEC sname: covered by: *.openshift.gnome.org. -> *.openshift4.gnome.org., new TTL 2716
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][cache ][07606.20]     => NSEC sname: empty non-terminal by the same RR
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.20]     <= answer received:
                                       ;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 27790
                                       ;; Flags: qr aa  QUERY: 1; ANSWER: 0; AUTHORITY: 0; ADDITIONAL: 0
                                       
                                       ;; QUESTION SECTION
                                       openshift4.gnome.org.                DS
                                       
                                       ;; AUTHORITY SECTION
                                       gnome.org.                  16        SOA        ns-master.gnome.org. hostmaster.gnome.org. 1649348977 600 900 86400 3600
                                       gnome.org.                  16        RRSIG        SOA 5 2 900 1651937377 1649345377 40692 gnome.org. D4nUm9bExjX/lUoG+TgMdYuccR7InE2wSzBLR2a4ocU3IqpNvA7seBmll9x706ImEZ1oxtvXTZbozEG7W1c7KIlo+vvSl4yoQgQl37VncHhfW5U6Q69v9o1XRuledjb7l16OtynblHXQkDmZDrT9vwX0BV6eoZ78QG84lBqpaFk=
                                       *.openshift.gnome.org.        2716        NSEC        *.openshift4.gnome.org. A AAAA RRSIG NSEC
                                       *.openshift.gnome.org.        2716        RRSIG        NSEC 5 3 3600 1651937377 1649345377 40692 gnome.org. j3xWiApwlF6XY64qJnXepFklLWWOHYpQFl1ZBtEhT0THnbMMgwOUmhzvpCbeWJaNRZiqMNGBLo1g+4gaOA3RpzULFjH8GyW0fuzpZ7qwZAgxUsa9/Ii5tj5rtYTv8zZFkqv9xoQVLfwx09r12Sjrpg/aoXnHs0LEbSkCJWC3lAQ=
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][iterat][07606.20]     <= rcode: NOERROR
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][valdtr][07606.20]     <= bogus proof of DS non-existence
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][resolv][07606.00] request failed, answering with empty SERVFAIL
Apr 13 07:30:14 torino kresd[1679506]: [reqdbg][resolv][07606.20]     finished in state: 8, queries: 6, mempool: 49200 B

It seems when it resolves successfully when forwarding is disabled, it caches the result and continues resolving correctly even when you re-enable forwarding. However as soon as I remove the cache, forwarding then fails again.

kresd.conf:

user('knot-resolver','knot-resolver')
 
net.listen('127.0.0.1', 53, { kind = 'dns', freebind = true })
net.listen('127.0.0.1', 853, { kind = 'tls', freebind = true })
 
net.listen('::1', 53, { kind = 'dns', freebind = true })
net.listen('::1', 853, { kind = 'tls', freebind = true })
cache.size = 256*MB
modules = {
  'policy',
  'view',
  'hints > iterate',  -- Load /etc/hosts and allow custom root hints
  'serve_stale < cache',
  'workarounds < iterate',
  'stats',
  'predict'
}
view:addr('127.0.0.1/8', function (req, qry) return policy.PASS end)
view:addr('::1/128', function (req, qry) return policy.PASS end)
view:addr('0.0.0.0/0', function (req, qry) return policy.DROP end)
policy.add(policy.suffix(policy.DENY, {todname('use-application-dns.net.')}))
policy.add(policy.rpz(policy.DENY, '/var/lib/rpz-downloader/urlhaus.abuse.ch.rpz',true))
policy.add(policy.rpz(policy.DENY, '/var/lib/rpz-downloader/threatfox.abuse.ch.rpz',true))
policy.add(policy.rpz(policy.DENY, '/var/lib/rpz-downloader/cert.pl.rpz',true))
policy.add(policy.pattern(policy.PASS, todname('uribl.com.')))
policy.add(policy.pattern(policy.PASS, todname('zen.spamhaus.org.')))
policy.add(policy.pattern(policy.PASS, todname('dbl.spamhaus.org.')))
policy.add(policy.all(policy.TLS_FORWARD({
          {'2620:fe::fe', hostname='dns.quad9.net', ca_file='/etc/ssl/certs/ca-certificates.crt' },
          {'2620:fe::fe:9', hostname='dns.quad9.net', ca_file='/etc/ssl/certs/ca-certificates.crt' },
 
          {'9.9.9.9', hostname='dns.quad9.net', ca_file='/etc/ssl/certs/ca-certificates.crt' },
          {'149.112.112.112', hostname='dns.quad9.net', ca_file='/etc/ssl/certs/ca-certificates.crt' },
})))
predict.config({ window = 20, period = 72 })
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