Nighthawk R7000 Slow WiFi speed

Hi!

I've been having some issues with my Nighthawk R7000 for quite some time.
I've googled and read contless forums on the issue but have never found any solution which has worked for me.

The problem is that if i run a speedtest on my LAN connection i get descent speed (about 200 Mbit/s u/l and d/l on a 1 Gbit fiber connection. I maybe should get more, but I can't say the router is to blame in that case).
However if I measure on the WiFi, I only get 20-25 Mbit/s on 5GHz and around 10 Mbit/s on 2.4GHz. This is when no1 else is streaming and when standing 3 metres from the router with full signal strength.

The router is placed so there should be low/no interference from surrounding equipment.
I've reviewed channel traffic and made sure the router is broadcasting on channels which is used by noone else.
I've made sure the antennas are correctly attached.
I've performed a factory reset and re-configured the router, same issue.
The currently installed f/w is V1.0.9.18_1.2.27.
I've also disabled things like vpn, QoS and guestnet to make sure no services or configurations will conflict/interfere.
I've disabled SmartConnect, same issue.
I've disabled coexistence for 2.4 GHz, same issue.

Any ideas on how to solve this?

PS.
I've done the speed measurement for my fiber connection using Bredbandskollen.se , which is the standard tool for measuring internet speeds in Sweden. The WLAN measurements was done using the same site on my Samsung Galaxy S7.
DS.