ok, have you tested speed between two client devices attached to the same AP and the same Radio (i.e 5ghz)? I use IPERF3 do to this task. using one in Server mode, and the other in Client mode may show you where your issue is.
I know it's very odd.. for it to be less than 2mbit for 2.4ghz..... I'm guessing you got the R300 used... .. as a comparison... do you have any other wifi access points other brands to test the 2.4ghz..... just to see if your area is that congested. If not you could have a bad R300 on the 2.4ghz... it just seems as if the antenna's on the 2.4ghz aren't really working.
Hello Hayk, yes, I had another AP from TPLink and it Works without a problem. Looks like the problem is with my 2.4 antenna the problem. I configured the 5GHz antenna without a problem and both APs are working perfectly for 5GHz, not for 2.4GHz