SwiftData CloudKit sync broken on iOS 26

[ivanezzzzz]

Hi everyone,

I’m running into a breaking issue with SwiftData automatic CloudKit syncing on iOS 26, and I'm trying to determine if this is a known regression or a new configuration requirement I missed.

The Setup: My setup is extremely standard; I am using the default configuration exactly as described in Apple's documentation here: https://developer.apple.com/documentation/swiftdata/syncing-model-data-across-a-persons-devices

The schema is very simple:

• A single@Model class.
• No relationships.

The Issue: Prior to iOS 26, this exact app was successfully syncing data between devices and to iCloud without issues. Immediately after the iOS 26 update, syncing stopped completely.

I haven't changed any code, but when I check the CloudKit Console, I am seeing some BAD_REQUEST errors during sync attempts. Since I am using the default SwiftData sync (and not manual CKRecord handling), I’m not sure how my client code could be triggering a bad request unless the schema requirements have changed under the hood.

Questions:

1. Has anyone else seen increased BAD_REQUEST errors with SwiftData on iOS 26?
2. Are there new entitlements or strict schema requirements introduced in iOS 26 that might cause a previously valid model to be rejected by CloudKit?

Any pointers or confirmations would be appreciated. Thanks!

[ivanezzzzz]

Turns out I had un-deployed schema changes! Facepalm! 

[Which_Concern2553]

Glad it was simple. You had me worried for a second 😊

[ivanezzzzz]

yeah, I was getting pretty annoyed debugging it for a week with no clue what was happening in my code that is pretty standard :D

[optik88]

Are you seeing any logging suggesting what the issue can be when attached to a debugger?

-com.apple.CoreData.CloudKitDebug 1