MT7603E 2.4GHz interface stability issues

I would like to bring up the topic of MT7603E stability in latest mt76 versions again.
It's inspired with https://github.com/openwrt/openwrt/pull/11220 and the upcoming switch of ramips target to 5.15 kernel.

I have been testing for a while a WF3526P / ZBT WE1326 device, equipped with MT7603E+MT7612E, with "kernel-5.15" openwrt from master — and experience issues with 2.4Ghz (MT7603E) interface stability.

The problem is that the WiFi connection is stuck at some moment of time, more likely when the load is increasing and much data is transferred over the wireless connection. The issue can be easily reproduced with iperf3 running within a couple of minutes.
When the issue occurs, a client stays connected to the AP (no visual changes), but no wireless traffic can pass the connection. There are no errors in logs both on the client side and on AP.
The workaround is to reconnect to the AP, and it proceeds to work until the next connection hang.

There are several tickets on MT7603E: #669, #576, #419, #411, #391, #390, #375, etc., they're probably related, but show different symptoms. Also, worth to mention:

• This is not a hardware issue. The device worked fine on openwrt-19.07 with uptime for more than a year, and no issues were observed;
• The issue presents already in openwrt-22.03, that's the reason why I've tried looking for the fixes in master, but to no avail;
• The interface works much more stable in legacy mode (802.11g), probably the issue is related to 802.11n proper support. I've initially suspected #576, but SMPS should be already disabled for MT7603E.

Start by reproducing the MT7603E 2.4GHz hang on the WF3526P or ZBT WE1326 with OpenWrt kernel-5.15, using iperf3 to generate traffic. Compare behavior in 802.11n and legacy 802.11g modes, and review the related issues #669, #576, #419, #411, #391, #390, and #375. Done means the connection remains usable under sustained load without requiring a reconnect.