@Hyroniemus 

Hi,

As the computer is only 5 meters away from the router, can you test if you get the full download speed when they are connected via an Ethernet cable?

If the download speed via cable was also reduced, then it could be due to some Antivirus software or "Security" software (like Avast, for example) that is monitoring all incoming data traffic on the computer. Such thing has happened before to other users.

  @woozle Already tried that. Full speeds while using a cable, around 940 up/down

 Well....not much support from TP-Link...

  @Hyroniemus 

Even though the download speed via cable is not affected, you may still want to check if maybe a software has installed some sort of packet filter driver or similar thing only for the network connection of the TX3000e. On a clean Windows 10 install it should look like shown on the screenshots below. In case you find additional "company xyz protocol / driver / whatever" things in that list, then deactivate them and test the download speed again.

  @woozle 

Nothing strange here...The funny thing now is that speedtest starts at around 800mbps and then drops to around 450mbps

  @Hyroniemus I had the same issue, installed the 3000 and was getting maxed speeds (1.2 gb download) from my 1gb connection.

This lasted for 2 weeks then lost full speed. It was giving me only wifi 5 speeds (max 800mb or so) even though my router supports wifi 6.

After investigating and trying so many fixes finally found a solution for myself.

Had to go into my ISP hub settings and rename the 5ghz SSID channel to something other than the 2.4ghz one (kept the same pw etc) .

Unticked the smart network button that seemed to switch between 2.4ghz and 5ghz adhoc and just had the 5ghz linked to the new SSID i created.

Then went back to my PC. selected the new SSID 5G network i created and max speeds again on wifi 6. 1.2gb download.

Not sure if this will help, depends on your ISP but fixed it for me.