Here's an oddball thing I encountered in LR Classic. It appeared that I had accidentally selected all photos and overwritten the keywording for every photo in the database with the same single word. I was expecting to have to restore from catalog backup. But, I closed LR, then relaunched, and all was well. Has anyone else experienced this?
I have made my share of mistakes with keywords but never experienced what you described above. I’m glad all was well after relaunching LR.