Trying to get 2.4 GHz working

Our beloved Ubiquiti wifi router seems to have died overnight, leaving us to start using the 2.4 and 5 GHz wifi built into the Comcast Business box installed in February.

5.0 GHz works perfectly, but we have some older devices that need the 2.4 GHz. All such devices will connect to that wifi, but none of them have connectivity. (The Windows devices specifically say "no connectivity" and are unable to troubleshoot the problem themselves.) I logged into businessclass.comcast.net because apparently that's the only option to adjust the wifi.

Resetting the wifi module on the router hasn't made it work, and that's trying both "reset wifi module" and "reset wifi router". Back on businessclass.comcast.net, when I renamed the 2.4 GHz network and gave it a human-readable password, the network simply stopped broadcasting. Turned out I'd somehow told it to hide -- so I told it to broadcast again, but you guessed it -- it's still not broadcasting, nor can I connect to it using "Other network" settings on any device.

Meanwhile I also turned off the public wifi feature in hopes of clearing the air a bit, but both of those are still broadcasting anyway. (True even when I reset the wifi router. Odd since I can't imagine our neighbors' networks are showing up at full strength inside our metal building.)