As i've said before, it only happens as I delete these specific objects. I've been adding obstacles in the form of immovable physics objects, since that's the only way I can currently do what I'm trying to do. Just now i've gone in and deleted EVERYTHING ELSE in this cap file but some objects that I had to remove to prevent the crash. It still crashes, so i've isolated it to those parts, and worked my way down from there.
It's apparently being caused by objects with these same characteristics: They use a custom collision, they're right triangles (and so is the collision), and their angle is NOT 0. I changed their angles to 0 and everything was fine. Then as an experiment I changed an object's angle back to what I had it at (90) and sure enough, it crashed again.