iphone 11 weird wifi problem

Help!!!!!

This problem is driving me crazy, when I connect my iphone 11 to my home 2.4g wifi, signal is full, but the network keep dropping off. Although wifi signal is on, it constantly getting zero speed for a short period of time, and then back to normal. All my other evices works perfectly at the same spots.

I even use the airport utility to detect the signal strength, it was around -70dBm on iphone, same as my another android phone and an old iphone 6s. I tried to restore network settings, using itunes on pc to restore factory image, tried everything I could, it just don't work.

The following youtube video shows iphone always disconnect for several minutes and then back to normal ,while android never had this problem with an even worse signal.

https://www.youtube.com/watch?v=yi75GHRXAyo&feature=share

And then I created a hotspot on my pc connecting to the same wifi, then the problem disappered.

Then I started to adjust router's setting

I pretty much tweaked everything I could, nothing changed I really don't understand what really casued this problem, and why it only happens on the iphone 11.

I don't think send it to an apple authorized service provider will resolve anything, they most likely will tell me it was my router's problem, because the problem is hard to recreate on their network, and obviously apple support will keep telling you to restore your phone and update software.

I highly doubt it could be a chip failure, but you know, nearly impossible to let apple take a look inside since the send for repair option don't even have a network failure description for you to choose.

I hope if someone was experiencing the same problem could provide a solution.