WiFi Slows Down on IPhone 11 Pro Max

I have had my IPhone since December last year and I have noticed that at times the WiFi slows down considerably when I am in the middle of browsing videos or using safari. I recently got a network testing app called Net Analyzer to check the speeds at these times and got these results from a recent test.

My home WiFi is typically at around 111Mbps but sometimes I cannot even get 400kbps for download speeds.

Upload speeds vary too with it being so bad as to not register anything on the test.

In comparison here is a screenshot of the WiFi during normal times.

While I am aware that position of router and the internet providers speeds do fluctuate, I have noticed though that the internet speeds suddenly improve if I turn off the WiFi on the IPhone and turn it back on.

However it is frustrating for me to have to keep turning the WiFi off and on, regularly as this can happen on a daily basis, sometimes 2-3 times a day.

Could you please advise me on how to correct this issue?

I have tried removing website data and cookies, restarting the IPhone, and I have even reset the network settings, but the issue still continues to happen.