I have 250 down and this happens to me every so often.

Everything starts lagging and buffering, I unplug and plug back in my router.

There is probably a faster way of going about it, but this way has worked for me 100 % of the time.

On Firefox i have the same problem. Even sometimes the video plays but the display of the video is black. It lags the videos are buffering at very start of a video for no reason. I know I have fast internet so it shouldn't happen. It started happening just after new year/

If its not a router problem check your Chrome Extensions by going to the top right hand side of your browser and clicking the three stacked rectangles, settings, then going to extensions. Sometimes malware can leak into your browser extensions if you download something that tries to stealth install malware, so if you see any funny looking extensions, delete those. To figure out how to permanently delete things like that, get on your phone(because youtube obviously is an issue on your computer) and look up a tutorial on how to remove malware manually. You can also try installing a scanning program such as malwarebytes.