Comment 6 for bug 1846760

That tells me the crash is happening inside the stringProperty function, but calibre itself does not call that function, ever. So it is something internal to Qt. If you can get a proper backtrace that might help narrow down the cause. I dont use ubuntu so not sure of the procedure for getting backtraces there, but on systemd based distros, something like:

echo bt | coredumpctl gdb