Two days ago I left the 'puter running overnight, in the morning the whole UI was grey, there was some sort of pop-up but it was off screen and I could only see the edge of the dialogue. Force quit and restart as normal.
Today getting ready to teach class the custom shelf - and only the custom shelf was greyed out. No pop-up. Restarting Maya showed the problem persisting. No time to search for a solution.
Apparently One Drive (the Real Player of the 21st century) can cause this - and lo and behold without any prompting from me Maya had backed itself up to One drive last night.
The fix for the shelf is easy, enable 0 should be enable 1 - but how is this happening just because I don't shut down Maya overnight?