I’ve tried both a soft and hard reset. Not sure the hard reset took, strangely. Xbox One and Firestick, various apps. Problem usually starts with some garbled/distorted dialogue from the rears and then the center (7.2 system). Cycling through the native, upmix, etc fixes it.
I also tried changing the 5G channel on the wifi but no difference.
May try another hard reset to see if it’ll take.
Hoping it’s not something more serious and just an odd foible like having to change inputs and back to get audio on Plex (only on the content not the menus and only on the Xbox One app, oddly).
It also has the odd habit of always switching from HDMI 2 to HDMI 3 (Firestick) whenever I choose Xbox One (HDMI 2) no matter how many times I reprogram my Harmony remote.
Not dealbreakers or anything, everything else is great.