Photos app uploading more photos than I have in my library
I'm looking for help. I have just (painfully, due to my slow internet) uploaded about 40 photos from my iPad into iCloud photos. Once home I did some basic editing, on the iMac, and expected to have to wait for some more uploading. Sure enough, initially it said 'Uploading 13 Items'. Unfortunately, after a few minutes this changed to 'Uploading 6380 Items' (and the progress bar doesn't seem to be going anywhere fast). What is odd is that I only have 5346 photos in my Library and have nothing in the Trash Album. I have tried repairing the Photos database (launching with Option and Command held down) - the same thing happens. My other devices and the iCloud website all show the 5346 photos I'm expecting, just without the last few edits. Any help would be appreciated - particularly as the 5000 photos in my library, when I "upgraded" to Photos from Aperture took 3 weeks to upload!
iMac, OS X El Capitan (10.11.6), 27" Late 2012