quitting on text manipulation

I've been getting this attached error/quit msg when trying to a lot of text work, e.g., changing fonts, all caps, tracking, line spacing in a lower 3rd.
Just now, I got it just by dragging the 'Custom' title to TL. (would be V3 over video and a graphic)
I'm all caught up with updates and just yesterday trashed prefs.
any ideas?
TIA

OK, reworded my search, and found this from Ronny:
"You get this message when your Project database is getting corrupted. It's a safety system built inside FCP X to prevent you from continuing to work on a corrupt Project and risking to lose all your work.

When you get this message you will see that you cannot use CMD+Z (Undo) anymore. That's why FCP X won't allow you to continue. Usually the problem has nothing to do with the exact clip or the title you are working on, it's a database issue.

The best thing you can do when you get this message is to paste the Project content into a new Project, as you have done. This will create an entirely fresh database for your edit and, unless there is effectively a corrupt clip in the Project, this will solve the problem."

Is this still the case two years later? And by 'project' do you now mean 'Library'? I was actually working in a CC, but one which happens to be part of a 'project'. I think I will delete that project completely.

I had the same message a couple of times last week working on a new project. FC restarts automatically and than the problem is 'solved'...... for a while. Sometimes I restart the iMac. During editing for 3 or 4 hours the problem occurred 2 or 3 times. I will make a new project and copy the project.

Peter

Specs:
2015 iMac 27", 5K Retina 8GB, 2TB Fusion, 2GB graph.card, external 250SSD (FCPX project drive)