I have seen this. I reported it to Apple.
It occurred to me that font problems might have something to do with it.
I went through my fonts both by looking at the preview in Photoshop and also in Font Book. The preview in Photoshop showed some fonts that would not show text characters in preview just empty “null character” boxes (not sure what they are called). Most of them were non-system fonts that I had installed at some time or another. I also had some fonts show up with problems in Font Book. I removed any problem fonts by disabling them in Font Book. Not sure at this point if this solved the problem but I haven’t had an issue since I did this.
You might try running font validation in Font Book to see if you have any problem fonts. It might help.
The other area that might be a problem is the title generator reverting to its defaults due to a bug. It shouldn’t do this but who knows. That’s why I reported it.
NT