I've seen where attempts to perform asynchronous callbacks yield undesirable results. For example -- I've experienced similar results with my attempts to use asynchronous callbacks to implement websockets. Looking at the documentation, there isn't any indication that DllCallbackRegister is limited to synchronous operations only. However, there is @Melba23's comment here from 10 years ago. This appears to be a timing issue because the callback will often occur properly without causi