Archer C6 router not working properly after connecting AC1200 Range Extender RE305
I had bought Archer C6 router in Aug 2020 and it was working perfectly fine with no issues whatsoever. Then in May 2021 I bought the Archer1200 Range Extender RE305 and it was working fine for half a day. After that the wifi kept disconnecting in the main Archer C6 router. The internet connection from the ISP modem was working fine, but the router Wifi was switching off and on every 2 minutes or so.
Then I disconnected the Archer 1200 Rabge Extender and rebooted the router, but the issue is still there. I am not sure how a range extender can make a router unstable. Even after disconnecting the extender and rebooting the router. Someone please help me.