Yeah, a clean install might be needed. I was on the phone for a free hour with Apple Support and they were confounded. I was the first to call in with the issue. Might be worth making a call to help build their case.
The first suggestion was to uninstall the FCP studio suite (using AppZapper, a third party app), and then reinstall.
If that didn’t work, wipe the drive and do a fresh OS install.
I’m finishing up another project before I try either. Will post my results here.