I have all my photos stored in Photos on my Mac (originals kept on device) and synced to iCloud. When I go to iCloud.com I can see all the photos so I know they are there. However some of the photos appear as only gray boxes on my iPhone or iPad. If I try to edit the photo on the phone it starts to download but then throws an error of “there was an error downloading this photo from icloud photos”. Searching online shows various people with the problem but no real solutions. A common suggestion was to sign out of iCloud so the photos are deleted off the phone then log in again so they get downloaded. I’m reluctant to try that right now due to a less than speedy internet connection. Anybody else seeing this problem?
What file format are the originals in?
All are in JPEG. Some had been edited and some are originals. All are older pix, Jan 2016 or earlier. All since then sync properly.
check if the file names are .jpg
Just checked a number of them and all are .jpg files. In one case a series of pictures taken over a few minutes had a few not synced to the iPad. Almost no difference in camera settings.
Then there is no other option then “Nuke & Pave” 