Found the solution for me on one of my computers. Something is being blocked and I’m pretty sure it is googleapis.com. If you use a DNS sinkhole or have your DNS pointed to a third party that uses a sinkhole, this could be your problem. Also this may be why disabling extensions may work too, especially if they are ad-blocking in any capacity.
Troubleshooting: Open a youtube video and start playing. Hit F12 for the devtools to show up. Click on “Console” and check if you see any errors (in red if Chrome) that have “goolgeapis” in their url (Example: POST https://jnn-pa.googleapis.com/$rpc/google.internal.waa.v1.Waa/Create net::ERR_NAME_NOT_RESOLVED). If so that could be the problem. As soon as I took googleapis.com out of my DNS sinkhole, video started playing normally again, and the errors for googleapis don’t show up any more.
Good Luck