RBR Repeatedly Self-Reboots After Upgrade to Firmware 2.6.2.104

I have an RBR20 that has been working very well in my house for a couple of years (installed Christmas 2018). We've had our share of blips, but for the most part I have been happy and getting reasonably reliable service and coverage.

Last week, it upgraded the firmware to 2.6.2.104 . 

Within a couple of days, I started having issues with random disconnects. Sometimes it just loses internet connection and wifi is still connected, other times the whole thing goes down. Eventually it got to the point where it would not keep a reliable connection for more than 10-15 minutes at a time.

I tried rebooting the RBR, rebooting the satellites, rebooting the cable modem (Netgear CM500) and no luck. I tried to revert the firmware, but it asks for a login / password to revert the satellite's firmware, and doesn't accept the router's regular login info, or even the default login. I tried reverting just the RBR's firmware, but then the satellites get stuck in Config Sync and won't connect. So I reflashed the 2.6.2.104 firmware.

Eventually, the RBR's password changed, even though I didn't change it. And again, the default password didn't work. So I did a Factory Reset with a push pin. 

Even after the factory reset, I could barely get through the setup without reboots / disconnects.

Finally, I gave up and reinstalled my old ASUS Router, and it has stayed connected now for several hours! Of course, devices at the "outer edges" of my home don't get a good wifi signal, which is why I went to the Orbi in the first place.

The changing of the RBR password makes me wonder if this was a remote DDOS attack, and maybe after rebooting my cable modem a few times it changed my IP. My ASUS router (and EVERY router I ever owned since around 1990) has an option to turn of ICMP to the WAN so my IP cannot be Pinged from the outside world. The Orbi has this option, but it's grayed out and can't be unchecked. WTF!?!?!

Or could it be something else?

How can I unbrick my RBR20?