Photos - unable to upload

Can anyone help me with the following issue, please?

I have been gradually uploading my Photos library to iCloud photos, which has been a slow, slow process because of bandwith and upload speed restrictions. Finally it appeared to complete, but I have been left with a folder entitled “Unable to Upload” that contains some 2,000 photos. Having checked via the web interface, these are definitely missing from iCloud.

Googling around it is suggested that the solution is to export the originals of these photos, delete them and then reimport them (Apple support article). This sounds (a) drastic; and (b) will loose all the edits, colour corrections etc. I have made. That’s a LOT of work to redo.

One suggested cause was that the files were not JPEG, but TIFFS in disguise (so as to speak), however this is not the case. The only commonality that I can see is that they have been edited using a plug-in editor. This makes me think the issue may relate to metadata; I have no idea what, perhaps something like the colour profile?

Any suggestions as to cause and solution would be gratefully received, or failing which alternatives to Apple Photos.

Thanks

Possibly an unrelated problem. Under Mojave I had two photos that wouldn’t upload. Unlike yours, Photos just kept trying and trying, saying “2 remaining”. I therefore could not identify them as you have been able to do, because Photos never finally deemed them “unable to upload”. When I finally installed Catalina they all uploaded.