This is still an issue for me in Xcode 15 RC. Below is an example of the transformer I'm using for saving a UIColor final class ColorValueTransformer: NSSecureUnarchiveFromDataTransformer { static let name = NSValueTransformerName(rawValue: String(describing: ColorValueTransformer.self)) override static var allowedTopLevelClasses: [AnyClass] { return [UIColor.self] } public static func register() { let transformer = ColorValueTransformer() ValueTransformer.setValueTransformer(transformer, forName: name) } }

I've also come across this issue too

If you mark the properties in Category as optional then it works fine with no crashes. But then you don't get uniqueness and you're able to insert duplicates into the context.