I spent quite a while testing this over the last few days and I’ve found the issue to be something with enumerating relationships. My app is a music app, so I have an Entity for Album, Artist, Genre, etc. Artist and Genre have a one-to-many relationship to the Album entity.
If I create all of the objects in CoreData (2500 Albums, 800 Artists, 250 Genres, on my test device) but DO NOT link any of the relationships, everything is able to successfully sync up to iCloud and download down. If I link only the Artists, syncing is also successful. No Artist has more than 5 Albums linked. Once I link the Genres to Albums, however, the crashing begins. I started playing around with this and found that if I limit the maximum number of Albums linked to a Genre to under 15, syncing is successful. If instead I make the limit 20, the crashing issue comes back.
I’m really hoping beta 8 addresses this. Starting to get quite nervous as the release approaches!