Having this exact same issue. If you follow Scott Manley's guide (
) here with the rover inside the 2.5m bay eventually this rocket will crash KSP on reverting from launch or to assembly. I tried building it one piece at a time, launch it, then check for a crash, and it doesn't appear to follow any pattern on when it crashes, just its a 100% chance eventually. Once it starts crashing it will crash every time afterwards if you revert. Annoying.