How to diagnose WiFi problem in Archlinux?

Question

linux

ThinkPad X220 laptop, card, respectively, Intel Corporation Centrino Advanced-N 6205 [Taylor Peak] (rev 34). Configured through NetworkManager.
5GHz does not see at all. 2.4GHz sees and connects, but does not work correctly.
The incorrectness is expressed in the fact that about once a minute the data transfer freezes. The connection to the point is not broken. If I try to connect to a point on a mobile phone - the mobile phone hangs deafly in a few seconds. If you don’t disconnect from it, it can hang tightly (I pull out the battery), if I have time, the phone comes to its senses in a minute or two.
It looks like the laptop is somehow heavily overloading the access points.
But here's how to figure it out and fix it - it's not clear.
Arch latest, updated. The problem also occurs when using an external USB stick.
There are no problems under Windows and Debian, everything works fine.