Every so often the contact sheet freezes and becomes stuck. I may have several sheets open, and the others work fine. I can click on images to enlarge them, tag them, rate them etc. However, when I switch to the stuck sheet I can't do anything, not even scroll down the sheet.
A restart helps. This has never happened in photo Mechanic but is quite common in photo Mechanic Plus. Common enough to be annoyed by it.
Correction: closing the sheet and reopening it seems to fix the issue as well.