I would understand if it were many for an individual. However this happens if there are 2 photos for a person or 20. I double checked and my grandson (in the attached photo on the OP) is only tagged in 7 photos.
One thing I have found is that if you let it 'sit and spin' for a minute or two and then cancel, often it will come right up. Not always but a lot. Sometimes that just results in waiting again.
So it seems like it is going through all photos for the site rather than just that individuals - at least at first. Or it is building some kind of cache and gets hung up and then when you cancel and restart the process it is done.
Am I the only one seeing this? Or perhaps the only one reporting it...
This is still an issue a year later. I am also seeing the same behavior that Tom described. If someone is only tagged in two photos, it can take just as long for the thumbnails to come up in the change photo window as an individual tagged in 30 photos. Although, the difference between Tom's problem and mine is that the hanging for me can last as long as three minutes. I'm patient (geneaology takes that and then some), but there are limits!
I got the FTB and sync'd my site with it. Now the photos for all of the people in my tree have been 'disconnected.' The FTB only recognizes new photo albums or the Family photo album. If I had chosen a personal photo for someone in say the 'Smith Family' photo album, FTB doesn't recognize them. Now I am in a worse spot than before. Day forward (pictures or albums I add now) works great but FTB doesn't sync all of my photos. It appears to not be backward compatible with existing photo albums.