Having the same issue with 10.5 and Mojave…
I was working on a project w/video for an hour or so, then the beachball pops up (noticed it when adjusting the standard EQ), then managed to stop it by clicking on the arrange window (then furiously hitting CTRL+S lol). Then it did it again, but longer… and managed to get it to the pointer again, but then right after, beachball again but it then locked up and crashed.