I, too, had a sudden drastic internet slowdown on my Win 10 pro which has been running very, very smoothly since I moved up from Win 7 about 6 months ago. My internet is a 100 Mb download through cable and router. Two days ago, in the middle of of surfing the net, I suddenly lost my internet connection. When I managed to recover it, I was horrified by the slowdown. Speedtest showed me that from my usual 90-95 Mb download I was getting less than 1 Mb!!!!
So I started googling and after 2 days of trying all the suggested tricks/hacks/fixes, including a repair reinstall and tearing my hair out whilst cussing all concerned, I was desperate and so backed up all my files and prepared to do a clean install.
Suddenly it occurred to me that maybe it was a hardware glitch on my router, so I called the tech. service of my ISP and within minutes we had solved the problem very simply.
He told me to disconnect the router from the electricity and also the "cable" cable. After ten seconds I reconnected the "cable" and connected back to the electricity and
Lo and behold my latest Speedtest tells me that I'm back to
97Mb download.
I'm not saying that this solution is right for everyone, but I am saying that we should always check the simple basics and ourselves first., before blaming the OS and/or Microsoft. I think perhaps being of the Analog Generation, I only look for nerdy/geeky solutions when I don't see the easy solution staring me in the face!
I was aware that occasionally there can be a static electricity problem with the hardware and it simply has to be re-earthed, but I didn't think of that and rushed into all the geek "solutions".
K.I.S.S.