[Solved] OpenWrt on MT7621/MT7615N devices with 5GHz problems

I have the same issue on 1 picky WPA2 2.4Ghz IoT device with really low data activity (dir-1960, OpenWRT21).
When with OpenWRT default configuration, it happens once every 6-7 days that Wifi on that device freezes. The client device then claims that Wifi is still connected, but signal strength on the device shows strength 0, data transfer stalled. Disconnecting and reconnecting Wifi on the device side itself reestablishes the wifi connection. This restarts the 6-7 day cycle.
Rebooting OpenWRT does not fix it, once the IoT device is in that state.

So far, my test status is:

  1. proprietary access point
    An exclusive decade old Airport Express access point hosted for that picky device does not cause wifi errors.

  2. Timed reboot of OpenWRT
    A nightly reboot of the OpenWRT router via a power outlet timer clock seemed to avoid the issue as well. But so far, I have just tried that for 2 weeks and have since moved testing effort to the following parameters as of now.

  3. option disassoc_low_ack (default 1)
    setting this option to 0 has a noticable effect: It round about doubles the period of flawless operation for the picky device to around 2 weeks. So this setting helps, but does not fully fix it.

  4. skip_inactivity_poll (default 0)
    so far, changing this option set to 1 does not seem to have an effect for my device.
    (The disassoc_low_ack setting being 0 in parallel)

  5. option wpa_group_rekey
    Since I have set this to 86400, it is the first time, that my 1 picky WPA2 IoT device had a flawless WiFi connection for 38 consecutive days on OpenWRT 21.02, before WiFi connection crumbled away again.

Interesting. I also have this bug on another device (iPad (WPA3, 5Ghz, same dir-1960 with OpenWRT 21). It appears rarely, so I was not sure so far, whether browser, modem or OpenWRT were causing this. But it does appear a lot less often with the previously mentioned Wifi customizations, probably as of now once a week on a single random http request, with killing and reopening Safari on the iPad fixes it. With default OpenWRT Wifi setting, it felt like appearing at least daily. Not sure if that is due to the same bug, but likely related.

Also very interesting. I will put that on my test bucket list.