Async Calls in ConnectToPersistentSubscription EventAppeared

No, in fact if you do this you could start handling things out of order. Something similar can happen when you have an IObservable of Task. If you really need async event handling, you will have to create your own queueing mechanism to handle it, and connect it to EventReceived.

Cool thanks for the quick response.

This isn't true with persistent subscriptions that he is using.
Instead turn off AutoAck and use subscription.Acknowledge directly in
your async callbacks. There also is no assurance of order with
persistent subscriptions (its try your best) so that should not be an