SP/coop play with bots can cause all sorts of unexpected errors, often causing a game crash.
Mostly it is caused by the bots using some equipment they never used before while testing, or reaching some area of the map without navmesh or one of the multiple other reasons..
Anyway, even without a error message from windowed mode, you can help by reporting at least during what map it happened and maybe some info about how far the game had progressed. This might help us to limit the areas we have to search for errors.