Lxc-attach error

I have Ubuntu 20.04 running in an unprivileged container (as root) in ALT Linux server (LXC 4.0.2).

When I try to execute “lxc-attach con1” I get an error:

lxc-attach: relocation error: /lib/x86_64-linux-gnu/libnss_files.so.2: symbol __libc_readline_unlocked version GLIBC_PRIVATE not defined in file libc.so.6 with link time reference

I can successfully attach to the container by executing “lxc-attach con1 – /bin/bash”.
I don’t know if this is related but when i try to install openssh-server in the container I get this (other packages have been installed correctly):

installed openssh-server package post-installation script subprocess returned error exit status 1
E: Sub-process /usr/bin/dpkg returned an error code (1)

I managed to install openssh-server after I got into the container with “lxc-console con1” command.