About a quarter of my 40,000 photos are missing in iCloud, and the older photos I do have are misbehaving. Apple Support insisted that I upgrade my laptop to the newest operating system before they could help me solve the problem. So I did, reluctantly.
It was a big mistake.
More later. I'm trying to do a full back-up, save all the old back-ups (that want to erase themselves), find those missing photos, and figure out a better way to store them so that they never disappear on my again. (Ha.) Then I plan to regress my laptop back to the older OS, which runs more smoothly on my 7-year-old machine. Even Apple thinks this is a good idea. (Ha.)
This is the photo that made me realize I was in trouble:
I took this in 2013, and it should be sharp at the usual size here. But something happened to the large, original file. This is as big as it gets. At least it still exists.