5ghz worse than 2.4ghz wrong setup?

Hi, sorry if wrong category..

I have new xiaomi router ac2100 the cylinder black one.

I have finished setup of openwrt and now i run into issues. My 5ghz band isn't working properly and only giving link speed of 72.2mbps. I have 120mbps internet connection on lan and the router have gigabit port. When tested on pc with lan i have constant 120mbps. However when using 5ghz the connection is capped ad 50mbps and sometimes drops to 30mbps while in the same room.

It seems to me that it doesnt want to switch to 80mhz on the RX side only stuck ad 20mhz.

Any fixes? Thanks