Yes, we did a support call, but they started going for the "reinstall" and all that stuff, so we basically ended the call. I've got both of the FCPX and macOS feedback tabs open, but I haven't reported it yet. Not very forthcoming of me, I know.
However, if anyone else is feeling lazy like me, you can do what I've started doing: Whenever FCPX gets into a beachball frenzy, you can force quit it, and as you do that, the error reporter pops up and asks why you quit it and asks you to reopen the application. I've done this quite a few times now. This could be a convenient way to bombard Apple with crash reports and messages describing why the app became unresponsive.
Let's hope there's a fix soon!
PS, another interesting thing I've seen on my 32GB machine is that the RAM doesn't seem to be used up more than about 55%. Throughout the issues iStatMenus has never plotted over 60% memory usage. Seems a bit odd. Anyway, sorry for the side track.