Old albums exist on iCloud.com but the same albums are empty in Photos

This has been asked several times and I have tried several things but I haven't found an answer that says, "Oh! This happens when [situation] and to fix it, you must [solution].

I have many years' worth of photos in iCloud. Many of them are in old iPhotos albums, which is a bit confusing but it's okay. However, those same albums on the computer are empty.

I have turned iCloud off and back on, I have upgraded iCloud to make sure I have enough space (there was a long time there where we had exceeded our 200GB plan but didn't really consider what that meant for our old photos), I have moved the library and re-linked to it in the new location.

After all that, iPhoto says it's uploading 8000 photos. I have no idea what's going on there, and hope there's some way to remove duplicates later, but I'm going to let it finish overnight, in hopes that that is only the first part of the syncing process and the missing photos will download.

In the meantime, here are a couple of screenshots to show what I'm looking at; there are probably 100 Albums with 0 photos.