Try to wrap your device/cable in aluminum foil. There's some interference on hardware side sometimes. I had to use this method every time I want to stream something from youtube though projector - speed gets so low that i get like 144p video.
btw, anyone has problems with wifi speed when microsd card is in use? When trying to use speedtest.net while copying files to microsd card (Samsung Evo+) test won't even start, can't get through ping stage Doesn't look like there are many users affected by this. It's not a big deal, but it adds to many things that I'll mention to Microsoft near the end of my warranty period when asking for exchange.