If sandboxing is failing then the cause will most likely be a kernel or glibc update that changes some syscall that the Qt sandboxing infrastructure uses.
And libiconv is a red herring. calibre runs with LD_LIBRARY_PATH=/opt/calibre/lib so libiconv will load fine.
Some googling will find you various hits:
https://bugs.launchpad.net/ubuntu/+s...c/+bug/1939993
https://forums.ankiweb.net/t/setting...-linux/13765/7