Chris After reinstallation program will need to perform complete index of your archive. That includes opening each file and recognizing faces on each one. If this was not done yet, you will not see those faces in your archive. Also, if for some reason you disabled facial recognition in your archive, faces will not be found and added to those personal folders.
So please make sure facial recognition is on, and just wait for indexing to finish. All faces will be back again.
