Hello, 

I recently purchased the Archer C6 and had a lot of problems with it so far. I have a cable modem without Wifi function to which the Archer C6 is connected. I have run the quick setup via the tplinkwifi website and then set the router into Access Point mode. At the beginning I was getting very bad speeds on all devices but after updating the firmware this issue resolved. Most connected devices use the 5Ghz network and the connection is fine for the most parts. 

One if the devices (Huawei mate 10 lite) however does not support 5 ghz and is therefore connected to the 2.4 ghz network and is getting very bad speeds. Speedtest are only getting 1/10 of the bandwith at best and Youtube videos etc. play at 240p max. 

What I already tried: 

Reboot Phone, Router, Modem

Forget and reconnect the wifi

changed channels to 1, 6, 11 and auto

used "smart connect" (basically everything on auto)

I keep most settings on auto or use the smart connect feature. 

Additionally while laptops and desktop pc seem to get stable 80-100% at speedtests, the phones connected to the network are reaching speeds between 20-80% most of the time and are much more volatile (meaning they are sometimes stable and sometimes all over the place). I dont know if this is an issue with the wifi chip in the phones or has anything to do with the router.