update:
In playing around with the devices to troubleshoot the service interruption/crashing error, I turned off AdGuard. Now AdGuard will not turn back on. The UI reports a DNS confirmation error conflict. (The device has default DNS settings; I don’t know what causes this error.)
I leave AdGuard OFF and the interruption/crashing has stopped.
note: the interruption/crashing was occurring with both firmwares 3.202 and 3.212
(AdGuard 0.107.5-1)