Rescan faces hangs up or very slow

I use rescan faces quite a bit. It used to work great, just a few quick seconds and it was finished and I could continue tagging on the photo. The last several months when I use it (I really can’t remember how long this has been happening, but quite a while) it doesn’t seem to work, or takes a very long time. If I stay on the same photo most of the time it never resets with the new face ovals to tag. If I switch over to a different photo and then come back to it sometimes it has rescanned. I just left it on a photo I had rescanned for a few hours while I ran errands and it still hadn’t done anything when I got back. I clicked rescan a few more times, turned photo tagging on and off, flipped back and forth to a few other photos in the set, and finally the rescanned ovals were back for me to continue tagging. Something isn’t quite right with it!