I'm using 2 Archer C6 v2 routers as wireless access points.

When the Archer C6 routers are disconnected from the main router, my internet connection is fine. However when either or both C6 routers are connected to the main router my internet connection is spotty and, I drop anywhere from 50% to 80% of my pings to 8.8.8.8 . Pings within LAN and to the Modem are stable.

They are connected to a main router (Ubiquiti Edgerouter X) that is connected to a cable modem. My test computer is a Macbook Air (M2) that is hardwired to the main router through  a dock via an Archer C7 acting as a switch.

Both Archer C6 routers are in AP mode and have DHCP disabled, and the Internet/WAN port is unplugged and connected to the main router through the LAN ports. The Archer C7 has DHCP disabled and the WAN port unplugged and WAN settings set to static and left blank.

I managed to fix it by connecting only one C6 router and disabling the 2.4ghz radio. I don't think it's a problem of the radio interference, as I could access the wider internet when the C6 routers were unplugged, but remained on and broadcasting wifi ssid.

Is this a known bug? I'd like to make sure that whatever underlying is issue fixed, and the disabling the 2.4ghz radio doesn't feel like a permanent solution.