Similar problem. I have at least 12 people defined in my photos but only one person appears when I try to select people in the Wallpaper photo shuffle (see screenshots below). I tried to troubleshoot by turning off the photo shuffle wallpaper and restarting my phone then turning shuffle back on. Before I did that I had two people show up as options so it made the problem worse.
Same issue as all but with a difference. I have hundreds of faces identified , only 5 came up. Chose my wife, but then she disappeared and now no pictures at all come up on lock screen. Please fix the bug, should not be hard to duplicate.