Thats definitely weird! I'm not sure when it will be available but it is mainly fixes, Nintendo Switch will be a new device type.
I've sent you a PM with something to try.
I don't have any specific recommendations for a wifi analyser unfortunately but should be some decent free ones online
Tried your advice in the PM but that made it worse so I undid that change.
Upload speeds are reasonably close to what they should be but download seems to be the main problem since they are less than the upload during speed tests.
That really should not be the case since I get 300 down and only 25 up. Sometimes I can get around 70 down but it comes and goes and is still less than 1/3 of the speeds I should see.
Checked wifi analyzer again and router seems to be selecting the least congested channel. I really don't have too many strong wifi networks nearby though.
You didnt disable WMM did you? Also when you said you erased from admin settings have you tried a factory reset using the button at the back of the router? I found that I had better results using that for a factory reset than using the one in the menu for some reason, and at this stage it could not hurt to try that way then set up using, no back ups. I would try Also don't turn on 160Mhz or untick 20/40Mhz coexistence leave them as they are. Unless you have faulty hardware that's what I would try as a last resort.
I don't normally disable WMM but I did try it just to see and didn't make any difference in my tests.
I used to do the factory reset by using the button on the back but after the second or third time I did that (during previous firmware upgrades) the button got broken so I can only do it from the admin settings now.
I did not try to load any saved settings when I reset to factory, I always just adjust the settings I need to (such as qos).
I left all wifi settings as default but when I didn't get expected speeds I tried changing some different things. Some made it worse and some made it a little better but nothing has been able to give me anywhere close to the 300 down that I should be able to get close to. I have tried with iPhone 8 and gaming laptop with ac wireless adapter.
I will try to see if I can get the router to do a factory reset using the button on the router but can't try to fix that now because family is using the internet.