I have the same issue, on iOS 18 and MacOS 15 I can't delete an item. My item has relationships. It's working on iOS 17.5. Also, I have the same issue when modifying an sub-item in my item. Here are the logs: Thread 0 name: Thread 0 Crashed: 0 libswiftCore.dylib 0x00000001946291a8 _assertionFailure(_:_:file:line:flags:) + 264 (AssertCommon.swift:147) 1 SwiftData 0x00000002524066a4 _FullFutureBackingData.getValue<A, B>(forKey:) + 780 (BackingData.swift:494) 2 SwiftData 0x0000000252406cb4 protocol witness for BackingData.getValue<A, B>(forKey:) in conformance _FullFutureBackingData<A> + 24 (<compiler-generated>:0) 3 SwiftData 0x00000002523a579c onOptionalArray #1 <A><A1>(_:) in PersistentModel.remove<A>(_:for:on:) + 316 (PersistentModel.swift:414) 4 SwiftData 0x00000002523a7340 specialized PersistentModel.withRelationship<A, B>(from:to:by:onModel:onOptionalModel:onArray:onOptionalArray:onCodableArray:onOptionalCodableArray:) + 1060 (PersistentModel.swift:0) 5 SwiftData 0x00000002523a82d0 specialized PersistentModel.remove<A>(_:for:on:) + 892 (PersistentModel.swift:421) 6 SwiftData 0x00000002523a62b0 onOptionalModel #1 <A><A1>(_:) in PersistentModel.addToInverse<A>(of:on:) + 524 (PersistentModel.swift:468) 7 SwiftData 0x00000002523a66b4 guardAndInvoke #1 <A><A1, B1><A2>(_:with:) in PersistentModel.withInverseRelationship<A, B>(of:from:to:onModel:onOptionalModel:onArray:onOptionalArray:onCodableArray:onOptionalCodableArray:) + 60 (PersistentModel.swift:521) 8 SwiftData 0x00000002523a68fc closure #2 in PersistentModel.withInverseRelationship<A, B>(of:from:to:onModel:onOptionalModel:onArray:onOptionalArray:onCodableArray:onOptionalCodableArray:) + 180 9 SwiftData 0x00000002523a7a94 partial apply for closure #3 in PersistentModel.withInverseRelationship<A, B>(of:from:to:onModel:onOptionalModel:onArray:onOptionalArray:onCodableArray:onOptionalCodableArray:) + 28 10 SwiftData 0x00000002523a70a4 specialized PersistentModel.withRelationship<A, B>(from:to:by:onModel:onOptionalModel:onArray:onOptionalArray:onCodableArray:onOptionalCodableArray:) + 392 (PersistentModel.swift:559) 11 SwiftData 0x000000025239fdfc PersistentModel.withInverseRelationship<A, B>(of:from:to:onModel:onOptionalModel:onArray:onOptionalArray:onCodableArray:onOptionalCodableArray:) + 776 (PersistentModel.swift:524) 12 SwiftData 0x00000002523a1f90 PersistentModel.addToInverse<A>(of:on:) + 1252 (PersistentModel.swift:487) 13 SwiftData 0x00000002523a3128 closure #3 in PersistentModel.setValue<A, B>(forKey:to:) + 816 (PersistentModel.swift:237) 14 SwiftData 0x00000002523ff5bc RelationshipCollection.enumerateModels(_:) + 392 (BackingData.swift:50) 15 SwiftData 0x000000025239f8c8 PersistentModel.setValue<A, B>(forKey:to:) + 1516 (PersistentModel.swift:234) 16 WriCo 0x0000000100a55754 closure #1 in SchemaV1.StoryScene.tags.setter + 136 17 WriCo 0x0000000100a54d5c closure #1 in SchemaV1.StoryScene.tags.setter + 36 18 WriCo 0x0000000100a815b8 partial apply for closure #1 in SchemaV1.StoryScene.tags.setter + 16 (<compiler-generated>:0) 19 libswiftObservation.dylib 0x000000026b469e2c ObservationRegistrar.withMutation<A, B, C>(of:keyPath:_:) + 100 (ObservationRegistrar.swift:364) 20 WriCo 0x0000000100a7f098 SchemaV1.StoryScene.tags.setter + 120 (@__swiftmacro_5WriCo8SchemaV1O10StorySceneC4tags18_PersistedPropertyfMa_.swift:12)