I have the same problem as well. Windows 10 was "forced" upon me, which I tried and experienced many problems (e.g. brightness). I switched back to Windows 8.1 and have been having wifi connection or "Windows-could-not-detect-this-networks-proxy-setting" problems ever since.
Yes, I checked and all drivers are supposedly up to date. As a reference, without any change, e.g. new ISP, I was streaming on youtube and netflix at 1080p only a few months ago. Now I am streaming at from 144 to 480p on my PC, while freely streaming at 720p (at least) on my PS4 or phone that are connected (wireless) to the same router.
I don't use proxy and I have checked many times that it's set at auto. I'm just a regular user who mostly streams and surfs youtube, netflix, google news and look at facebook and twitter.
Microsoft, PLEASE ADVISE and FIX THE BUGS. Thank you.