UPDATE:
@CrashXRu is awesome! Our router like totally forgot its own identity after the attack. He had our gt-ax11000 back up and running in under 5 minutes, even better than the day it was bought. He's helped out a lot of members here.
If you SSH these commands and they end up returning nothing for each, then your router was hacked or zombied somehow and needs some reconfiguring:
ATE Get_DateCode
ATE Get wBom
ATE Get_HwId
ATE Get_HwVersion
ATE Get_PINCode
ATE Get_ModelName
ATE Get_SerialNumber
ATE Get_ TerritoryCode
Thanks again CrashxRu (Ruslan^2), you're a tremendous asset to this forum.

(His Telegram QR Code is attached below)
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OP. (Saturday, March 29th):
In the sinking boat with my GT-AX11000. Thanks so much for this report!
Mesh broke down, after a few years of solid operation. Out of nowhere the AX11000 factory reset itself. After that, can't re-establish mesh, and srarted having issues with self resets every half hour or so when memory runs out (actually sat and watched as crazy cpu going on and memory bar went to %100), and intermittent wifi. Only 5g-2 (N,AC,AX160) currently usable after a few hours each time installing firmware trials / factory resets. Almost looks like it would work fine with all radios at first, but then loosed 5g-1, and eventually 2g. I tried disabling those radios for now in Pro settings, but get the Country Code missing error.
Have an Orbi-mesh running until a possible fix is found.
I'll try getting ahold of CrashXRu