Asus RT-AC 3200 slow speed on 2,4 ghz wifi

[Nokas2004]

Hello hello, i need some Asus expert help. I have 350 x 350 mbit internet line, fiber optical. And I have the Asus RT-AC3200 with the Merlin 380.66_6 firmware. Wired network from Asus router direct to pc (windows 10) give me 350 x 350 mbit speed. Also on both the 5 ghz wifi I get 350 x 350 mbit speed on my ipad close to the router. BUT, the 2,4 ghz wifi only give me 110 x 110 mbit.. I have tried switch chanal, switch brandwitch on 2,4 band. But nothing helps. 2,4 ghz wifi give 110 x 110 mbit, and 5 ghz wifi run imediately up to 350 x 350 mbit. What am I doing wrong??? I also tried to restore factory defaults on my RT-AC3200, but no luck.. Tried on several units, iphone, ipad, windows computer, but same on all units.

Regards
Norway