Hi all; I’m the original poster of this thread.
I gotta admit, I was surprised when I received some e-mail notifications that there were people responding to this old post of mine. I couldn’t remember, so I had to go check: I originally posted the first message of this thread back in December of 2020 
From looking at the continuation of this thread, goseecal, was it you that perhaps did a Search on this forum and came across my post?
And then, boy, a bunch of others replied after that.
Well, just to let all of you know:
In December of 2021, I posted another message: https://community.tablotv.com/t/vpn-buffering/28588
To sum up that post, roughly around January of 2021, I relocated my Tablo unit (the Quad) to my home office; I have a coaxial cable that runs from my roof-mounted antenna into the home office. This is also where I have my DSL modem. So, this way, after reconnecting my Tablo unit to the home office and connecting the coaxial cable in there, I was also able to hardwire the Tablo unit with a Network cable directly to my DSL modem (download speeds are between 80 and 85 Mbps).
So, after launching the Tablo app on my Roku Ultra player in my livingroom and accessing the Tablo unit, I adjusted the Live TV Quality and Recording Quality, and I was able to put it at its highest setting of “HD 1080 - 10 Mbps, 720@ 60fps”; no buffering 
And then almost a year later - in December of 2021 - I started seeing the little spinning buffering circle again.
There were no changes made on my end to cause this: no more devices added in the household that would draw on the bandwidth. And, it’s not as though, say, someone would watch Netflix AND watch Tablo on another device at the same time; no, it was either one or the other.
So, I had contacted Tablo Tech Support, and then, posted that message that you see in the link I posted above. In that post, I thought perhaps that the VPN that I sometimes use on my desktop PC was interfering somehow. But no, I don’t think that was it…
Since then, I tweak around with the Settings in the Tablo: Sometimes what seems to work is that I have the Live TV setting set high - HD 1080 - and then the Record quality a little lower at 720.
I don’t know…even though firmware updates get released from time to time to the Tablo unit, I still think the problem is with the Tablo app itself (I’m referring to the Roku app; when I use the Windows version of the application on my desktop PC, I don’t see any buffering).
DiverDan: You mind saying which company/ device brand of OTA tuner/ recorder you switched to?
Pez