@Mexiak 

Hi,

In case you haven't done so already, then you could try the suggestions from this thread: https://community.tp-link.com/en/home/forum/topic/825108. It should also apply to the non-Plus model.

However, as you can tell from the comments in that thread, those suggestions don't work for everyone.

If you still have the possibility to exchange the TX20U for a different model (but not another "AX1800" USB Wi-Fi dongle, as it might use the exact same chip), then perhaps that would be the best solution.

  @woozle I returned the adapter. I think I'm going to get a PCIe one instead, but I'm not sure which one to pick yet

  @Mexiak 

That's a good idea.

Provided spending a few extra bucks is no problem, I would recommend a PCIe Wi-Fi card that includes a separate antenna mount with extension cables. 
Antennas that are directly mounted to the Wi-Fi card's slot cover can be detrimental to the card's performance.