I started using Lightroom Classic CC 8 (Imac version) a month ago. I have run face recognition through all 85,000+ of my photos. It worked great. In the last week, it stopped trying to perform any face recognition at all. After a new import, I always get "No people found". This is despite the "Edit / Catalogs Settings / Face recognition / Automatically detect faces in all photos" being checked.
I have toggled it back and forth, and the setting no longer appears to have any effect when I import new pictures (selfies just taken from my smartphone).
Sometimes, the face recognition will run the next time I restart Lightroom. Sometimes not. It is not very consistent.
I have the same preferences and it should be working. It seemes that sometimes LR is adding new faces but mostly nothing happens.
I didn't turn of LR on my Imac for one day and one night but ony one face was added with face detection and I know that a lot of faces should be recognized.