I have fixed a few crashing bugs post 2.42.6e in the shot routines (more Long - Single type mismatch overflows) which would manifest this unreproducability in re-loaded sims since shots arn't saved. That would be my bet for what you are hitting, especially if it is sim with lots of shots...
Don't spend too much time trying to track it. 2.42.7 should be out this weekend I hope...