Archer T9UH V2.0 download speed all over the place all of the sudden
So I bought Archer T9UH V2.0 several weeks ago, and everything was okay until a few days ago when the adapter started acting up.
Basically, I have 150/15 Mbit connection speed, and while I am completely aware WiFi will never be as stable as ethernet, this shouldn't be normal behavior.
During the first days of usage, the speeds were between 130 and 145 Mbit. But since a few days ago, those speeds extremely vary. Between 5,15, 30, 50, 70, 100, and the download is extremely unstable. Sometimes, the download just freezes for a second. Etc.
I'm connected via 5GHz to my router which is about 10 meters away from my desktop PC.
I've noticed that other users have similar problems. Is this a hardware or a software issue? Is the adapter overheating?
Edit: this is how it looks on Speedtest.
Thanks for help and advices.