Turris 1.x migration is broken because of broken updater from Turris OS 5.1

Migration on Turris 1.x fails once new updater is running. Version from Turris OS 5.1.0 terminates with following error:

2020-09-01 16:57:50 info updater[7673]: src/lib/logging.c:206 (log_subproc_open): Running postinst of liblua
2020-09-01 16:57:50 info updater[7673]: src/lib/logging.c:206 (log_subproc_open): Running postinst of libubox
2020-09-01 16:57:50 info updater[7673]: src/lib/logging.c:206 (log_subproc_open): Running postinst of libuci
2020-09-01 16:57:50 info updater[7673]: src/lib/logging.c:206 (log_subproc_open): Running postinst of libuci-lua
2020-09-01 16:57:50 info updater[7673]: src/lib/logging.c:206 (log_subproc_open): Running postinst of updater-ng
2020-09-01 16:57:50 info updater[7673]: transaction.lua:239 (fun): Removing packages and leftover files
2020-09-01 16:57:51 info sshd[8029]: syslogin_perform_logout: logout() returned an error
2020-09-01 16:57:55 info updater[7673]: transaction.lua:252 (fun): Cleaning up control files
2020-09-01 16:57:56 info kernel[]: [  152.998627] pkgupdate[7673]: unhandled signal 4 at b7ec2060 nip b7ec2060 lr b7eb16b0 code 30001
2020-09-01 16:57:56 info updater-supervisor[]: pkgupdate exited with: -4

Clearly it is problem that packages in Turris OS 5.1.0 on Turris 1.x are build differently over those in Turris OS 3.x. It has to be investigated why actually updater uses illegal instruction and if that is some CPU mode or if that is just issue that is present in Turris OS 5.1.0 as well.