POTENTIAL BUG:
Just restored to 13.1.2 as I was having issues.
Before I restored, I checked my photos app to make sure everything had synced with iCloud and at the bottom of my photos list it showed the correct number of photos and said “Updated Just Now.”
However after the restore and everything finished redownloading, it shows that nothing had uploaded for the past two weeks! I even checked iCloud.com and sure enough, none of my photos from the past two weeks were uploading despite my phone saying they did.
Just wanted to share my experience as this could potentially be a big big.
Photos also has a massive mug with curation and twins where it keeps merging tagged photos together.