Hi, So I re-flashed 386.12_6 back on and ran a factory reset, added the ISP and Wifi settings, left 5Ghz wifi at default settings after 20mins no SSID was showing, I checked and by default the DFS was ticked so it was using Channel 100 , so as you suggested Ive tested on a couple of channels 44 & 48, which got the 5Ghz accessible again, which is weird why on .11 and previous firmware Auto mostly used either channel 64 or 100 and was accessible from my devices.Control channel 64 is in DFS range. Use 36-48 or 149-161 (if available) only and test again.
Does this same router work properly on latest available stock Asuswrt firmware? I know it's EoL model, but for testing purposes.
Is this a hardware issue or incompatible with the newer firmware?
I havent used an Asus stock firmware for a couple of years, but I will try that also