Thanks to @PAR for reminding me of our previous discussion.
Your UPnP Server disappearing once a week is exactly the symptoms of your Ethernet Switch filtering OUT multicast service discovery packets from your dCS. That’s why the UPnP Server disappears.
When you unplug/replug the Ethernet cable from your dCS, the AQVOX Switch Port detect the device’s unplug and resets it’s multicast filter table, and so multicast packets flow properly again and the UPnP Server reappears. But sooner or later the AQVOX is going to again filter out multicast packets, and your dCS will not see the UPnP Server once again.
I definitely agree with @Phil suggestion, replace that AQVOX with a Netgear GS108 (basic model, not GS108T or any other alphabet after the “108”). Won’t cost you more than $40 new or so, or pick one up from eBay for $20 or less.
Solve that problem, and I suspect your other problems might also disappear.
I’d really like to get your underlying network issue sorted as I think that’s the big one here but if the no sound during playback persists after that then we’ll definitely be diving into the logs … I’m just cautious of pulling logs and getting the software guys here looking at them whilst we have a known issue that COULD be a contributory factor.