Justin, it's Jack from DSNY Newscast. I can't believe that another member of the Disney YouTube community is having the same problem with FCPX. haha
Ok, so I got the issue to go away by doing a completely clean wipe of FCPX. I mean not just deleting the app, but using Clean My Mac to wipe everything, and be sure to also get rid of the library files, and any plist files in the Movies/Final Cut Pro folder.
Then do a restart, clean PRAM, and restart and install again.
It is definitely tied to old deprecated files being broken. And not being removed when deleting the app. Hope this helps!
Also I'm still experiencing crashes on FCPX 10.4.9 on starting up FCPX, the only way I've found a workaround the crash is as soon as the app window opens, start clicking on the event file library, and it should not crash.
Apple really need to fix this. It's very annoying.