[Terretta]

The production iOS 9 cloud restore 'bricked' iCloud photo sync from my devices (iCloud Photo Library, not Photostream which was fine).

iCloud Photos wouldn't update on the devices because iOS 9 thought the devices were still restoring from backup. Apparently a known issue with tedious workarounds involving mounting phone as a drive.

iOS 10 beta fixed the issue (perhaps expectedly, as it wouldn't make sense to preserve a pending iOS 9 restore after update), and all the iCloud Photo Library syncs worked again.