It's not the Bolt or the TV (but you already knew this...)
Xfinity Flex (it was, cough, free, cough) is shutting the TV down via CEC, reloading an inexpensive enterprise switch causes approx 3min40sec network outage, which is long enough to cause the Flex to shut the TV off approx 4min20sec after the reload starts.
Maybe this will help someone else: If the Bolt HDA didn't fail, I probably would not have suspected Tivo and done the testing without posting here. I did see the posts about the Stream shutting off the TV, and others posts griping about this software rev as being buggy, and I followed in their foot steps, incorrectly.
Q: What other unexpected things were learned, investigating this? (bundling the HDA failure and the TV turning off when the network goes down issues togther)
A1: Blocking the Bolt from accessing the Internet doesn't make it happy (it won't load channel or guide data until it recovers, or I didn't wait long enough for it to load a old copy out of disk cache, IF it will...) but it will play recorded shows.
A2: I think I know what to do if the TV starts spontaneously shutting down now, thanks to youtube.
A3: TE4 unashamedly started pointing us as users toward streaming, I didn't really grok this, but I'm getting a clue. I hadn't been focused on local TV until the pandemic hit, now 6mths in, I'm paying more attention to it. I soooo appreciate having a deep cache of recorded shows to dip into if the opportunity presents itself, and supplement that cache of recorded shows with a streaming subscription of two. I need to do some TCO calculations on buying an Edge vs Channels Plus to educate myself better going forward. I kinda wish I hadn't bought the Bolt 2 years ago, but if I can get another 2 years out of it, it I should be on the positive side of break even on TCO... le sigh
A4: IF Tivo can execute on the Stream (steady progress on features and functionality) and it becomes *the* integrated guide Android device, with lots of filtering options, I may have to agree with the marketing guys and give it a spin... Tivo remote + Android TV over apple's too strong opinions for me.