Thanks, no worries, I'll try under the Wine to run windows version. But on my system I can confirm that after around hundred (from 80 to 150) of turns it happens on every game I tried for now. Once it even unfreezed after the country was destroyed in rebellion and city changed the duchy, but not sure if this was really the reason, because can't reproduce.
The wine version doesn't really work, if memory serves (I seem to remember it didn't load fonts so no text appeared). I'll throw together a testing build and try to track down this issue tonight.
Okay, I'm afraid I literally can't reproduce the bug. I can play fine for an arbitrary number of turns with no issues at all. Maybe it is something to do with your version of Ubuntu. I'll look around a bit more, but this might be a Unity thing which is beyond my control.
oh, ok, no worries. I don't check wine yet (maybe with PlayOnLinux there is a chance to run it), but in any case thank you for your investigation. In worse case will try something like VM or docker instance for challenge :D