Thanks! Yes, I definitely did not clear the protection history and the only thing that appeared was in the photo I shared.
A mystery indeed then...
Despite using it a lot since I got it Friday evening, the only other time the AVR shut down by itself unexpectedly was yesterday evening when I manually selected 'check for updates' last night and got what I now know was a 'false' 'firmware is available' notification.
I should have ignored it since I had successfully updated it Friday, but clicked on' update firmware' in case something new had been posted and then the AVR shut down (it displayed a message that it would shut down for the update, but it shut down fully (not just in standby mode which would have had solid red indicator light next to the power button).
After 15 minutes I pulled the plug and put it back in and it booted up fine and when I checked for firmware again, it showed the latest version was installed (which I had ALREADY installed successfully Friday).
While everything with the AVR works fine other than this one-time firmware notification glitch (some kind of software bug or unstable AVR firmware code), I may reset the AVR to clean out any odd issues, especially since I suspect some eARC / HDMI CEC bug / glitch due to an apparent Android TV and / or Hulu app issue.
Too bad since I had it set up nicely in terms of settings and Audyssey which I reran yesterday for my Atmos speakers.
I did notice my Sony XBR77A9G TV (bought brand new in Dec. but eARC had never been used on it till Friday when I got the new receiver) has been acting up a bit since Sunday for the following audio issue (fixed with a TV restart, followed by a receiver power down etc):
Android menu navigation gets muted (supposed to have a clicking sound) and Hulu (and Amazon) sound stop accordingly at the same time (got a new Hulu app notification on the TV yesterday or Sunday night
after the sound issue happened).
Note that the Netflix app audio on the TV still works fine even while Hulu (and Amazon?) do not, so I know it not a sound issue or HDMI cable issue; perhaps some issue with the TV's latest Android update only affects some apps and / or a potential eARC / CEC integration bug or power saver issue.
Or Hulu is the culprit.
I read about eARC issues online with this TV on reddit, but those were mostly in the past I thought (summer / fall before a Sony Dec firmware update).
Going to record my settings and probably reset both the TV and receiver. And I will also check all the TV's eARC / CEC / HDMI integration settings again. It may be due to a bug with a combination of settings I chose which it does not 'like'.
Well, it looks like SEVERAL others also have audio issues with their A9G the past 2 or 3 days per another A/V forum, so there you go...