My device had to be dud. I got an replacement and restored a settings backup and everything has been working fine since then on my 2.4GHz network.
Not quite sure what warrants this hostile tone.
So return it as defective! If you have so many devices unable to use the router, why keep playing with it? You must know what you are doing if you are installing third-party firmware, so call it defective and get another one that works like it should. And add your clients back one at a time in case one is defeating your network.
I've deployed six 86Us and none of them have a 2.4 GHz band issue. I setup the WiFi and the devices connect. Done. WiFi doesn't require playing with all of the settings.
OE
Not quite sure what warrants this hostile tone.