I am not very experienced with core data or iOS dev in general, but I can recreate this problem at will and it's been driving me mad. I may well be doing something stupid, but for what it's worth, I can recreate this problem in my own app that I was developing and from just taking the demo app that comes with the CloudKit database and pointing it at the public. When I run the app for the first time, it works fine, up to the point that I disconnect or stop the run in Xcode. After that both my app and the demo app won't work unless I wipe the app completely and reinstall. Restarting the simulator or my iPhone makes no difference. I occasionally, but not always, get the Custom Zones message. I have no custom zones and I am only using the public database - this wasn't always the case, but I had to keep chopping down my code trying to figure out what was wrong. I always get the Custom Zone error when testing with the demo app, after starting a second or later run. Please feel free to point out if I am doing something stupid. I have cut my data model down to the bare bones and created all the indexes. partial errors: { com.apple.coredata.cloudkit.zone:__defaultOwner__ = <CKError 0x6000036e0ba0: "Server Rejected Request" (15/2027); server message = "Custom zones are not allowed in public DB"; op = 260E01FFE47D29BC; uuid = 5DCF73D3-1C3D-40AD-A3A3-29A6D509D0E2> }>}

Hi iOSDevDaniel Thanks for taking a look for me. But the issue I am hitting is not because I have created a custom zone, because I haven't. There are no custom zones in the test case above, and this distilled case above will work until the app is stopped and restarted. My best guess is that it's something to do with the sync. So unless there is some kind of custom zone created behind the scenes that I'm unaware of, and that I am somehow inadvertently using it, I don't think this is the cause. Thanks again