I've a network that is powered by an Airport Extreme and extended by an Airport Express. My Airport Extreme broadcasts 5 GHz and 2.4 GHz channels separately.
2.4 GHz operates on channel 4 and 5 GHz operates on channel 44. The network is WPA2 protected. 'Router Mode' is off. 'Radio Mode' is 802.11 a/n - 802.11 b/g/n (Automatic). And my 'Country' is selected to United States.
Also everything, including my network gear and things that connect to it, is up-to-date. And I'm not on any other DNS.
Recently I made the Airport Express extend the 5 GHz channel instead of the 2.4 GHz one because of 5 GHz's better performance.
But now when I connect to my 5 GHz channel I get worse performance than my 2.4 GHz one.
Below are the screenshots of my tests on both of the channels. The faster one is the 2.4 GHz one. (by the way, I know it's a shame but unfortunately that's the situation in my country at the moment, hopefully there will be fiber soon)
What exactly is causing this woeful performance on 5 GHz? What am I missing here?