Hello, Is replying that late still useful ? Maybe... So, is the following really ok ? NSError* error; // UNINITIALIZED completionHandler(error); If I understand Obj-C correctly, error will contain garbage since it is not static and not initialized explicitely. Calling completionHandler(error) with a non nil value will probably make macOS think that some error has occurred in startFilterWithCompletionHandler: calling `completionHandler(nil);£ may fix the issue. Marc