Given the infrastructure you already have, If I were you, I would place an Archer C6 in AP mode in the bedroom (Cat5E cable) connected like: VR2800 (LAN port) => C6 (Internet-blue port). Thus you...

That should be placed as a sticky note in the forum (using the blue port when the router is in AP mode as well) - I've seen a lot of people suffering the same issue - I just wrongly assumed from the...

Are you using the latest FW for your AX50 ? Try to upgrade if you're not. Then try factory reset and reconfigure from scratch. After that connect ethernet cable that way: ISP(LAN port)=> AX50...

In AP mode you can't set DHCP for Internet interface. Just make sure your ISP device is connected to the blue (internet) port of the AX50. I am using the same scenario.

The default GW should be the DNS. Look what IP address you receive for the GW, when in DHCP mode. Then switch to static IP and put that IP address for the GW. Just to confirm - you are using bluet...

Some of the new model routers have only QoS feature to restrict traffic. If you don't see Bandwidth Control in the main menu, but you have QoS then that's the case.