My ipad was not downloading photos from icloud photos, and was stuck uploading xxx photos. I tried turning icloud photos (and photo stream etc) on and off, and restarting the ipad, with no change in behavior. I then turned off icloud photos, deleted every photo off the ipad, turned it on and noticed that now, it says it is uploading 5 photos. These photos appear to not exist (the library is empty, the deleted files album is empty, and i have removed all albums, and are not visible either using image capture or windows) and I presume this is the source of my sync problems.
I then backed up the ipad, and restored from backup, and the problem persists.
I have one thing left to try that I can think of - restore as new and re-install from scratch - but this will be painful. Can anyone suggest an alternative?