@jonty oh god it was SO WEIRD
he's got a new solar inverter and battery setup.
it's doing some sort of weird backwards-ass network switching onboard, where it acquires an IP address over DHCP but then has a second IP at whatever the last DHCP-assigned octet is times 4. and then it sends so much UDP broadcast traffic that it kills the router's DHCP service and prevents anything else from getting an address, even though everything with an IP can route just fine.