Logic Pro X Timeline display

I seem to have a new bug in Logic Pro X 10.4.0, where the timeline display, which I like to set to "non-musical grid" or just straight hours, minutes, seconds, gets scrambled. At the beginning of my project, the display is correct, but after an hour or so the numbers are scrambled, don't make any sense. Closing the project and re-opening can temporarily fix the problem, but it comes back. I have tried trashing my prefs, same result.