I searched our bug tracking system and found a bug report some years ago from one of our beta testers.
He reported an engine crash and the attached log file looks quite the same as the one I currently get.
The only difference: The first room was another one (but the one that was loaded and where the crash occured was the same).
Good: So I guess I don't need to search in the first level.
Bad: If it's in the game code, why is it always the same level where this sporadic crash occurs ???
Hmmm ... strange.
I think my next step is to place both characters in the rooms where the game crashes in my savegame and check if I could reproduce the crash right after starting the game. Usually who have to play the game about 45 - 60 minutes to reach those rooms. So there happened already a lot of stuff at the point of my savegame.