I was going along fine (though very slowly) and had 5000 photos identified as my son. Hours later I was down to a few handful of photo and did a select all and dragged then to my son's named photo. After that I can still see all the photos of him, but Lightroom does not look to detect face on any of the pictures. I tried Photos--> People and all is greyed out. The first run through it detected them (until I did the Select all) and all the photos are still there. It is like Lightroom does not think there are people in the picture and there are , or it thinks that it already analyzed them and will keep doing so.
Is there a way to tell Lightroom to re-analyse this folder (5k of photos) to look for people again. Lightroom seems to have forgotten the Face Regions?
All the other proper in the 5K photos are designed correctly.