@jimas I tested it so far on my phone, mac, and ipad and all have full signal strength for both the 2.4 and 5Ghz bands

@terziyski 

Thank you for your input but it didn't work. I've tried limiting even to only "a/n" but no difference except much slower speeds. I am fairly certain that it's not the interference since there is only one other house close to me and my previous router worked fine. I tried also changing the channel a couple of times, same result. I've look on this forum and seen that there are other people with similar problem with the same router. I picked a couple solutions from there like changing the wifi name, channel width, disabling the 2.4 band, restarting the router after every change (which is annoying since its cutting the internet to the cable for a short period) but still no positive results.

@Kevin_Z The same behavior happens to the guest network. 

After switching to WPA2-PSK and rebooted, the 5Ghz stopped appearing in the Wifi list on all my devices (the 2.4 one showed up) and after a few minutes of refreshing, it appeared again but its way slower than before. Yesterday I was getting 300 to 500 Mbps on 5ghz and 800+ from cable, and after switching to WPA2-PSK i'm getting at most 130 from 5ghz and still 800+ from cable. I tried multiple times with the same local servers as yesterday. I guess it an improvement since it seams to not drop anymore but it's not really that much faster thant the 2.4Ghz band in which i was getting around 80Mbs.