cAP ax 5 GHz not working

I did another reset and it did kinda work this time
so if I set the frequency on 5g to any or all bands between 5170-5250 the SSID comes up. If I include any frequency after this e.g. 5300 the SSID disappears again. What exactly is going on here?
P.S I’m not an expert in wireless, especially mikrotik wireless but I do have a fair understanding.

Also, the speeds are not very good for me compared to my old TP Link Archer A9
I have a 300 Mbps internet plan and usually get a little extra (320-340 Mbps when using Ethernet or the TP Link router). With cAP ax, it initially shoots upto 320 but then gradually drops down and stabilizes around 250-270
I’m yet to do an iPerf test for a more reliable test