Keywords not syncing properly with iCloud Photo Library
I have three devices, a Mac Mini, an iPhone and an iPad. All are up-to-date (Mac Mini is on the 10.10.4 first beta) and all have iCloud Photo Library enabled and Photo Stream disabled. The Mac Mini is where all my photos are stored, so I have 'Download entire library' or whatever enabled. The iDevices are both switched to 'Optimize storage'.
I am going through the process of updating keywords on the photos on the Mac Mini so that I can get rid of the concept of albums and just search by keyword and location. This works fine (although after half an hour of doing it, adding a new keyword tends to make Photos hang for a minute or so until I close and reopen the program).
The issue I have is that these keywords aren't being updated on my iPhone (new photos sync eventually, but not as fast as on the iPad). So if I search on my iPhone for a keyword I've added since I switched on iCloud Photo Library, it doesn't show up in the results. Everything is fine on the iPad; things are updated immediately and I can search by any keyword I've added, even if I only added it in the past 24 hours. So I'm guessing the issue is with my iPhone.
I've already disabled and re-enabled iCloud Photo Library twice and it seems to update the keywords to that point, but then any new keywords I add won't sync.
Does anyone else have this issue or know how to solve it?
iPhone 6, iOS 8.3