"New" Orbi from Amazon gets 404 errors on setup

Bought an RBR50 base + satellite off of Amazon Warehouse. Ostensibly only the packaging was damaged. The satellite appears to be functioning -- I can connect to the web interface there. However, the Orbi app and even attempts to directly connect to the base via wired and wireless connections result only in 404 Not Found errors popping up.

I've tried resetting it with a safety pin and have gone through that rigamarole, no dice. It seems like perhaps someone *did* open this before and maybe messed up the firmware, as it kinda seems like the internal web server is messed up. (I'm assuming that's why I'm getting the 404s).

The wifi is working -- I can see the SSID. I can connect to the wired ports. It's handing out DHCP addresses and even pairing with the Satellite (seemingly). It's just that the web interface does nothing other than throw 404s.

Does anyone know of a way to upgrade the firmware without being able to connect to the web interface? Is there perhaps a way to do it via the USB port?

Or, shy of that, anyone have any briliant ideas on how to get it to work? Thanks.