Everything was going fine. Photos for OS X successfully uploaded and synced media across devices. My iPhone successfully optimised the media and edits / syncing was working smoothly for days. Then suddenly, for no reason, iCloud stopped syncing to and from my iPhone. Ironically, I could still view photos and they would still download a higher resolution version for viewing and editing. But syncing changes? Screw that, baby. Apple. It just works. Like a fat cop in a donut store.