OK I was able to fix that by replacing my DispatchQueue with a DispatchSerialQueue and using queue.asUnownedSerialExecutor() instead of creating a custom Executor. But I'm still worried about iOS 17 support given @eskimo 's comment. So I'll try to find a workaround. There are a few mentioned here: Actor `assumeIsolated` erroneously crashes when using a dispatch queue as the underlying executor.