Seems like this is back with iOS 18 & 18.1 (so far...). I had to reset everything for my app in the production environment so wiped the iCloud data, reset everything then reinstalled and imported my data into the primary device (iPhone) Sync completed after a day or so, then I installed the app on the iPad. Sync starts and appears to be doing something then nothing appears to happen for a while (maybe 20 minutes), then the app crashes again. No further data appears to have been downloaded. This happens every time I restart the app. Sigh... It's as though it's trying to do 'everything at once' for the initial sync instead of incremental syncs in small batches... and then it drops out. EDIT: Apple censored the word for 'drops out' that I used (ie. the thing they drop from planes) and substituted it with five asterisks - seriously? What puritanical nonsense is this??

Quick Update (Note: I've not received any official update from Apple yet) I've just installed iOS 15.2 (beta 2 19C5036e) today and have noticed that data now seems to be uploading from my App (App Store version) when previously it would just sit there... then crash. If I look under iCloud -> Manage Storage -> MyApp I can see the figure for data stored going up slowly. Better yet, I'm seeing data come DOWN to my other devices now. I'm not near my development setup so I can't test this on a physical device to see what the console output shows, but I'll try and do this tonight on my iPad. I'll ingest my large external backup file into Core Data and see if it uploads to iCloud and report back. There is no new update for Xcode yet so I don't think we can test with iOS 15.2 (beta 2) in a simulator environment. I'm not going to count my chickens just yet...