MT7603e does not handle SMPS well, making 2.4GHz WiFi disappear or system crash or connection unstable or lost

I have two SSIDs on the 2.4G WiFi, and sometimes they both disappeared after seeing these warnings.

My assumption is that sometimes the PS status of a client is not updated successfully, and the router side still keeps the old PS status, which could potentially make WiFi connection unstable. So setting htmode to Legacy/None to disable SMPS feature introduced by 802.11n could really help to solve the issue.

If my guess is correct, setting mode to Legacy may help. Partially

After applying https://github.com/easyteacher/mt76/commit/d287c0566819047999f0852f7e20ecde5030bc0e I found that the warning can always be triggered when my laptop with Intel AX200 is connected to 2.4G AP with power saving on.

1. Make sure Power Saving is off by sudo iwconfig wlp2s0 power off, and then disable WiFi on the laptop.
2. Reboot the router
3. Wait until the router finishes boot, and ssh into the router from another device like a mobile phone.
4. Run watch "dmesg | tail"
5. Enable WiFi on the laptop, and connect to the 2.4G AP.
6. Run sudo iwconfig wlp2s0 power on
7. Watch the output from the SSH terminal. The message should be there, which can prove that mt7603 does not set SMPS status to the correct value for the first time (mt76_poll returns false).

	if (mt76_poll(dev, addr + 2 * 4, MT_WTBL1_W2_SMPS, enabled, 5000))
		sta->smps = enabled;
	else
		printk(KERN_ALERT "set SMPS status failed.");

[ 1071.819628] set SMPS status failed.
[ 1071.934222] set SMPS status failed.
[ 1072.001711] set SMPS status failed.
[ 1072.160566] set SMPS status failed.
[ 1072.235204] set SMPS status failed.
[ 1072.323898] set SMPS status failed.
[ 1072.807554] set SMPS status failed.
[ 1073.353395] set SMPS status failed.
[ 1073.659795] set SMPS status failed.
[ 1073.799971] set SMPS status failed.
[ 1073.870927] set SMPS status failed.
[ 1073.949431] set SMPS status failed.
[ 1074.031043] set SMPS status failed.
[ 1074.103286] set SMPS status failed.
[ 1074.202853] set SMPS status failed.

Start with the MT7603 SMPS update path containing the shown mt76_poll call, then reproduce the warning using the listed Intel AX200 power-saving steps and monitor dmesg. Trace why the SMPS status update is not observed; done means the warning no longer occurs during the reproduction and the 2.4GHz connection remains stable.