Since we have a new dedicated thread for the "sync batching backend".
When this one is used, the traditional Executor which was always used before is never needed, but it's still being started.
In the opposite case of someone configuring an "async backend", the traditional Executor will be used but the new thread is being started anyway.
The correct behaviour should be to start either one or the other, never both.
Also useful to add some more logging to this component.