For anyone else having the same error, I fixed this by explicitly setting cloudKitDatabase: .none in my CloudKit-enabled app: let schema = Schema([Entry.self, Group.self, Category.self, Allowance.self, RecordMetadata.self]) let configuration = ModelConfiguration( "Default", schema: schema, isStoredInMemoryOnly: inMemory, groupContainer: .automatic, cloudKitDatabase: .none ) let container = try ModelContainer( for: schema, configurations: configuration ) It seems that the simple ModelConfiguration(isStoredInMemoryOnly:) constructor was using the .automatic CloudKit DB and for some reason, creating an in-memory container with .automatic CloudKit DB fails...