Missing albums after importing iPhoto Library into Photos.app / iCloud
When the Photos app was released, I downloaded and installed it and migrated all of my photos from iPhoto into Photos. I additionally enabled iCloud Photo Library so that all of my pictures could be stored online.
When the initial data import was complete, everything looked fine in Photos on the Mac - then the upload began. Around 8,000 photos and 400 videos.
Over time I have noticed that several of the imported iPhoto Albums / Events that were imported successfully at the time have disappeared from any device which is hooked in to my iCloud Photo Library. This includes an album of over 3,000 photos of my daughter, plus a couple of albums of work nights out, and albums I used to filter photos for making calendars. As far as I can see I haven't lost any "Smart" Albums - just manually created ones. I don't know off the top of my head how many are gone without opening iPhoto and comparing the lists side by side (I still have the old library backed up) - I assume, if required, there would be no risk in doing this as the library files are completely separate?
The photos themselves still exist in the library - thankfully - but the albums I created are gone. How - if possible - can I get them back?