Thank you for noticing! I'll provide some code, but in the mean time: Did you look at the last image in the other thread? The code is crashing on an optional parameter, but the expanded macro is failing on a different, and non-optional parameter. The only difference between the two schemas is that I have added a property in the newest, I haven't changed properties from optional to nonoptional

Thank you for your reply. I realized this is actually a duplicate of a previous error I posted about: https://developer.apple.com/forums/thread/765423

Thank you for your reply! This is actually a duplicate of a previous post. After a migration in SwiftData, some of the migrated databases (but not all) fail in fetching the backingdata for the models. The first frame on the stack trace is as mentioned an assertionFailure, and I have not been able to reproduce this consistently, which is why I have problems providing a code-example. See https://developer.apple.com/forums/thread/765423 for details of a similar crash