The levels are very small (just rooms in a mansion).

I tried something like that (mini main function):

level_load([first_room]);
wait(-5);
level_load([second_room]);
wait(-5);

In this case the crash didn't occur, but I'm not sure if this is a useful information. If it is an issue with a texture or model inside one of the levels, would this always lead into a crash? I guess that it might also depend on the total memory consumption, doesn't it?