I had another crash while using the key to unlock the last room in thieves' test. When I reran the game, it asked me if I want to load the crash backup instead - which I did, but the door was still locked and they key was not in inventory anymore. I had the game properly saved before attempting to use the key, so I tried to reproduce the crash, but it didn't happen again - and I tried several times.
Yes there were an error message - a longer one, which I forgot, but if there is a way to see all possible error messages I would recognize the one I got.
Sadly, I have overwritten the saved game before that door, that is why I was hesitating to report the crash since I don't really have much information to provide about it.