https://forum.test.turris.cz/t/slow-wifi-and-bad-signal-finally-solved/7372/21
Finally found above, exactly the same problem I have currently.
My setup is same since I installed msata ssd to the rightmost slot and moved 2.4GHz adapter to the leftmost, and 5GHz remained in the middle as it was.
So if I move 2.4GHz adapter to the middle slot will it solve the problem?