ONE X suddenly won't connect to 2.4 GHz, but accepts 5 GHz networks

My ONE X had been using the same 2.4 GHz (home) wifi for 3 years+.

Then I connected it to a 5 GHz network, once.

Then I tried to reconnect it to the home wifi, when it said:

*Connecting to "[home wifi]" wifi network*,

*Checking connection*

and after loading for far longer than usual

"Couldn't connect to your wireless network"

I have done EACH & ALL of the following:

- restart console

- power cycle console (hold power button, unplug power until "dead", plug in power and start up)

- factory reset console

- check router for filters of any kind

- unplug, power up and restart router

- factory reset router

==> NONE of these worked!

When I connected to my phone's 2.4 GHz hotspot:

=> same exact issue, no difference whatsoever

When I connected to my phone's 5 GHz hotspot:

=> I can connect to the Xbox Network, update system OS and do everything else, albeit with NAT type "strict" & worse connection.

I have also done the following:

- connected PC keyboard to type out password (should make a difference, but I tried regardless)

=> worked ONCE, then I shut down & started up ONCE, and it went back to not working

- change DNS

=> worked ONCE, then I shut down & started up ONCE, and it went back to not working

- repeated aforementioned step

=> NEVER worked again

==> over a month of this later and NOTHING has changed, despite two OS updates and several further attempts at everything listed

My other devices, including a ONE S, have no issues connecting to the same wifi network.

The ONE S has gone through the exact same change of recent wifi networks at the same time, including the change to the "foreign" 5 GHz wifi and return to the home wifi. I had disconnected both, transported both, set both back up and connected both to the other wifi. The same goes for disconnecting, returning home, setting up and connecting to the home wifi.

Only the ONE X refused to connect to the home wifi.

How likely is it that my ONE X's 2.4 GHz "antenna" is broken?

EDIT 01:

I've also tried clearing MAC, and had already set up the ports for Xbox Network and specific games, when I first set up the ONE X in my home wifi.

:)