Thank you. Please refer back to my original post. The ethernet dropping out was back in January, long before the current "upheaval in Broadband use". The buffering issue was a problem also since January and only occurs with Wifi, not with Ethernet. Additionally, buffering issues do not (and have never occurred) on our 2 iPhones, 3 iPads, and MBA. The buffering problems only occur when we use the apps installed on the Apple TV. There are no buffering issues if we stream from those same apps installed on our other devices (over Air Play/screen mirroring) to the Apple TV even during this time of "upheaval in Broadband use".
When the Ethernet was dropped back around Jan 7, 2020 I was referring to the Apple TV "putting itself" into the WiFi mode without me changing it manually in Network Setting. In fact, when it changed over on its own to WiFi, there was no Ethernet option under Network Settings. In order to again see Ethernet as an option, I would Restart and then go to Network Settings and select Ethernet. It could not "find/display" the ethernet connection choice UNLESS I did a restart.
The dropped Ethernet option and auto switching over to WiFi would only occurr when going into (or coming out of?) "sleep" or "rest mode". I knew it was no longer in Ethernet mode because the apps didn't work until they were "confirmed" again. Meaning I needed to verify my logins for each app either by entering my email and password or by entering the displayed URL in my device's browser.
At first I didn't understand the need for reconfiguing the apps so often. I was flummoxed by this behavior for about 2 weeks after purchasing the Apple TV. It was my first 4th gen model and it was quite different then my 3 gen models. Between endlessing configuring the same apps, the apps not working (loss of Ethernet) and auto disconnection from the BT speaker (a separate frustrating issue still occuring) it took me two weeks to sort out how a 4th gen HD model should work as opposed to discovering that some of the behaviors I was experiencing were not considered "expected or normal behavior".
Over the next 2 weeks (in early January), I finally tracked down the continual need for app logins after noticing in the Network Settings that app reconfiguration was always tied to the fact that the Apple TV was no longer using Ethernet. At that point I unplugged the Ethernet cable thereby forcing it to use only Wifi. After doing that I noticed that I never had to re-enter the app login information (unless I replugged in the Ethernet cable).
Next, I did an internet search and found this behavior (auto switching from Ethernet to WiFi) described by other 4th gen owners with a "hoped for" firmware update to roll out.
The next firmware update occured for me in mid February. I then reconnected the Ethernet cable, reconfigured the apps to work again and was hopeful the problem was fixed. But later that day it entered rest mode during non use. When I "woke it" with the remote, the apps requested me to log in again and sure enough, when I checked network settings it had changed itself back over to WiFi mode. I then disconnected the Ethernet cable and since then the apps have worked without a need to reconfigure their login. It has continued to restart itself since then (mid February) using the WiFi signal and the Ethernet cable has never been reconnected.
I very much appreciate your suggestion to contact Support and I plan to do so if a factory restore does not resolve the issue. If it continues and if Support does not offer a fix for the dropped Ethernet issue, I will drive to the store I purchased it from and exchange it. Fearfully, I have read incidental posts from others that a replacement unit did not solve their dropped Ethernet issue so I am weighing that in my decision as well. I am very curious if you own the same model and if Ethernet is your default connection within a WiFi enabled environment or if your suggestion has resolved this problem for another user in my situation.
I suspect that only a very small population of 4th gen HD Apple TV owners actually connect over an Ethernet cable when in a WiFi environment any more which would make it difficult for Apple to know how widespread the problem is.
Given what I know now, it makes sense that the first thing to try is a factory restore as "Quick Post" suggested in his reply to me. If I enable the connection setting solely for Ethernet and ignore the input request for a Wifi password then it may resolve the auto switching connection behavior. Since posting, it's not been easy to find the time to do a factory restore as we are home 24/7 and either the Apple TV or the connected TV set screen is in use all day, every day. The buffering issues are minor compared to the time involved in going through a restore. At least for the time being.