I had the same error. Right click on your SwiftData Model class name and Refactor to a different name. There are some Model names you can't use. Xcode never warns you, it just produces an error.

Ok, I think I figured it out. So.. when you generate SwiftData Objects from Core Data and if you have Transformable Data like above what I've done with an Array of Strings, you will get @Attribute(.transformable(by: "NSSecureUnarchiveFromData")) var yourArrayOfStrings: [String]? However, SwiftData is so good that it already recognizes these Array of Strings so having that Attribute confuses Xcode to thinking you're using NSKeyedUnarchiveFromData. The solution is to just delete that attribute like so... var yourArrayOfStrings: [String]? And it just works! The warning goes away in the Debugger.

It seems with a new Xcode update, the app doesn't crash anymore but still produces the error every time the variable is read from the model. So in a view when it's repeatedly read. The error floods my debugger and doesn't stop.

Here is what the Transformer looks like in the CoreData version of the app. I tried changing to @Attribute(.transformable(by: "NSSecureUnarchiveFromDataTransformer")) too.

Same issue with my transformable array of strings in Xcode 15.2 and iOS 17.3. I'm switching from CoreData to SwiftData and using NSSecureUnarchiveFromData. But still get this error and then the app crashes due to memory. Frustrating I can't move to SwiftData after all of the work I put into changing my code. Good thing I saved a copy of the CoreData version. https://developer.apple.com/forums/thread/744688

Same

Same

I had to go back to a UIViewControllerRepresentable as a temporary fix till this bug is resolved.