uPnP discover uses 1900, from what I have seen, everything else uses port 80
you may need to enable uPnP packets to flow through also, there UDP Multicast packets on IP address 239.255.255.250
All figured… My Fault, I had an incorrect response, even though it looked ok. Took running wireShark on the PI to find the problem. Double HTTP Header set, the first one was masked and the esp/Arduino code had it buried in the web server code. I have a few other methods to write before posting my code like Notify, UnSubscribe, Delete etc, but that’s just a time consuming formality, I will monitor all 3 devices over a few days to see if any drop out of control as the original poster was asking about. I do notice that the WEB UI;s do get out of sync every now and again and it takes a refresh of the web pages to get them all working again and staying in sync
Regards
Peter