Turning wi-fi off and on improves the speed

[TykeArt]

I have Sky Broadband Ultrafast Plus, 500Mbps avg. speed, Guaranteed Minimum Download Speed 400.0Mbps. After booting the PC I get Wi-Fi speed of about 200 Mbps but if I go into Settings>Network & internet and turn wi-fi off and on the speed improves to around 500Mbps.

Could anyone tell me what is happening and what to do to stop having to take this action to get top speed?

Thanks

[Jonothan2]

I am finding my sky Internet is just rubbish lately. My internet just drops out a lot. Especially on sundays strangley.

[TimmyBGood]

@TykeArt 

In crowded airspace, typically that's forcing the router to switch wireless band to a less congested one: the problem is that neighbouring devices switch in response and speed drops again.

Note that 'top speed' is obtained over ethernet cable: WiFi is very unlikely to do so.