@Sunshine, I have tried the followings: - changed LAN ports on the main router (did not help) - put a switch between the main router and my Archer 6, so now I have the following configuration:...

My Archer C6 V4.0 router operates in Access Point mode, it drops the internet connection (WLAN and all ethernet ports) many times. I have to reboot the router to get the internet connection back....