Youtube 1080p videos blurry

Solution
check your monitor cable connections secure ... it can be knocked out by cats/dogs/legs. Check temps of system. ensure you got at least 18GB free on your ssd (this is for windows pagefile growth).
On PC? Could be a bad connection to the server. On mobile/phone? Could be getting choked by your carrier. Despite the laws on net nuetrality, for now, carriers like Verizon have very recently been nailed for throttling connections to youtube and netflix.