Impossible to connect to EX7000 when it is connected to internet

EX7000, with factory defaults and stock firmware. Connected on ethernet to setup as wifi extender. Settings are saved (using a different SSID and password, 5G band disabled), device does its thing, lights go green, supposedly now connected to the internet.

At this point, NOTHING will ever connect to the EX7000 again. Two computers and a phone cannot hit the 2.4G band (android: perma "obtaining IP address" until "disabled, poor connection"), even existing wifi connections to the extender will be forcibly dropped. The best part? Neither computer can even connect to the extender on ethernet any more.

The only possible solution is to reset the extender AND ensure it is NOT connected to the internet. Multiple iterations of this mess have happened, with various levels of factory resetting in between. Firmware upgraded to 1.0.0.50 and tried a few more times. Nothing I can think of works.