keymgr not working after update to 3.1

Hello,

after update my knot installation from 3.0 to 3.1, the keymgr utility is not working anymore. How Can I find what is 'invalid item' ?

Thank you for your help.

root@ns1-knot:~# keymgr -l
Error: failed opening configuration file /etc/knot/knot.conf (invalid item)
Error: couldn't initialize configuration, please provide -c, -C, or -D option
root@ns1-knot:~# knotc -c /etc/knot/knot.conf conf-check
warning: config, policy[autoecdsa384].nsec3-iterations defaults to 10, since version 3.2 the default becomes 0
Configuration is valid
root@ns1-knot:~# dpkg --list | grep knot
ii  knot                           3.1.8-cznic.1~focal                amd64        Authoritative domain name server
ii  knot-dnsutils                  3.1.8-cznic.1~focal                amd64        DNS clients provided with Knot DNS (kdig, knsupdate)
ii  knot-module-geoip:amd64        3.1.8-cznic.1~focal                amd64        geoip module for Knot DNS
ii  libknot12:amd64                3.1.8-cznic.1~focal                amd64        DNS shared library from Knot DNS
root@ns1-knot:~#

strace:

...
openat(AT_FDCWD, "/etc/knot/knot.conf", O_RDONLY) = 6
fstat(6, {st_mode=S_IFREG|0640, st_size=48785, ...}) = 0
mmap(NULL, 48785, PROT_READ, MAP_SHARED, 6, 0) = 0x7fe07df6a000
madvise(0x7fe07df6a000, 48785, MADV_SEQUENTIAL) = 0
stat("/etc/knot/pri", {st_mode=S_IFDIR|0755, st_size=2418, ...}) = 0
access("/etc/knot/pri", W_OK)           = 0
munmap(0x7fe07df6a000, 48785)           = 0
close(6)                                = 0
write(2, "Error: failed opening configuration file /etc/knot/knot.conf (invalid item)\n", 76Error: failed opening configuration file /etc/knot/knot.conf (invalid item)
) = 76
write(2, "Error: couldn't initialize configuration, please provide -c, -C, or -D option\n", 78Error: couldn't initialize configuration, please provide -c, -C, or -D option
) = 78
exit_group(1)                           = ?
+++ exited with 1 +++