Camera upload not working?

I have our android phones set to perform a camera upload to my Plex server (running latest updates) whenever they’re recharging.

It sometimes works fine. Except that it “sticks” constantly on the last two photos taken, constantly cycling between them, saying “Two items remaining”, or sometimes actually INCREASING the count remaining as it attempts to upload the photos. The same issue occurs if I use the auto-upload function, or manually go into the settings on the Plex app & try a manual upload.

The most recent Plex for android patch was supposed to have addressed this according to the patch notes, but it still seems to be happening to me. I have two phones, and it’s occurring on both, so it must a configuration issue on the server I can’t diagnose?