@typeadesign 

There has been a couple of firmware releases since your current build in March. Update the router to the latest build 200929 and monitor the 2.4G to see how that responds.

@Tony 

Hi, Tony,

Thank you for your help.

My bad. My hardware is version 1.20. There's no option for that in the pop-up menu - it's either 1 or 2.

As far as I can tell, Archer AX20(US)_V1.20_200326 is the latest firmware update for my router. It was last published on 2020-04-09. Is there a newer one yet -- maybe a beta?

@typeadesign 

The sudden loss of signal sounds like maybe something else other than Wi-Fi channels since you scanned that.

Have you tried moving the router to another location as maybe an object or other electronic device can be getting to it?

Another variable worth changing is the channel width, and also lowering the power of the 2.4G.

@typeadesign 

I just purchased the same router, Upgraded to latest firmware : 1.2.0 Build 20201023 rel.69987(5553)

in under 24 ours it has dropped all 2.4G wifi twice. RF signal level is has been constant (-40dBm ), even when it drops connectivity I still see the signal. All 2.4G wifi devices cannot connect, I can try to reconnect on my tablet and same, unable to connect, no errors, just fails connection. and all my home automation devices go off line. Ethernet and 5G continue to work fine. Logging into the router and turning the 2.4G off, then back on, reestablishes all connections.  I purchased the AX20 to replace a more reliable but lower speed router, hope I didn't make a mistake. Any hints?

@RogerJT 

If any device on the 2.4G is static, switch that to DHCP. If the network is still up then there may be some sort of conflict happening. I would also try splitting the devices you currently have on the 2.4G network to the guest network.

@Tony 

A number of my devices are static and DHCP. All static devices are assigned out of the DHCP asignable block to prevent duplication. I have my DHCP block set to 100-200, and any static are outside that range.  Ip conflicts would not prevent network authentication!

When this happens, ALL connectivty on 2.4G is halted! All DHCP assigned devices fail, (which is pretty much all the home automationa nd security devices)

Even the static IP's fail. When this happens I can't even get connected on any 2.4G device, the 2.4G network refuses to even authenticate any device!  I can see the network and have no issues connecting to the 5G, full network access, but if I try to connect to the 2.4G, the connection fails! doesn't even try to authenticate!, just fails. Just says, "Connecting", then after a few seconds it fails.  I connect on the 5G and access the router and toggle the 2.4G off  then on, and everything returns to normal, all my devices automatically reconnect and function, and I am able to reconnect on 2.4G with the same device that filed earlier, with no issues!

I've also started my own thread so not to interfere with the original posters issues. but I believe they are the same,