Apple TV 4.4.4 Home Sharing no longer working over ethernet

My ATV home network setup has gone from working well to not at all over the last few days and I am trying to troubleshoot it, looking for folks with similar experiences. This appeared to start on or around the time I did the 4.4.4 update, though it could be unrelated, because at that time I also switched my main home sharing server from an old Windows laptop to an old Mac Mini I just aquired for that purpose (which is a sweet little machine for $250 btw).

Situation is, with the ATV connected via ethernet, it no longer sees any home sharing servers, that are on ethernet or wifi. It is also not available for airplay for any devices on wifi. This was working fine with the PC iTunes server on ethernet a few days ago.

If I connect both the ATV and Mac Mini iTunes server via wireless, it all works fine (but performace can suffer). Something has changed, as the ATV on ethernet was also fine to access my macbook on the wireless network a few days ago, but again it doesn't unless the ATV is on wireless too. Finally, the remote app on my iPhone will also only see the ATV if it is on wifi. To me it is like Bonjour is not working over the ethernet connection. I have done a little port prodding, and this appears to be the case, but it is not conclusive.

I have reset, restored to factory and re-updated the ATV, turned home sharing on and off a 100 times, cylcled the servers, reinstalled iTunes, all sorts of stuff.

Honestly, I would more likely put the blame on something weird with the wired vs wifi network routing on my XFinity router/modem, if not for the fact that I haven't touched it for months (save a few power cycles) and I just updated the ATV when this went south. I tried to ask Comcast about this issue, but that was like trying to explain quantum physics to the cat...

I've seen at least one other thread on this forum similar, was wondering if anyone else has had this sort of trouble since the 4.4.4 update?

Thanks