Recently I've found that on my youtube, none of the buttons show, these include the watch later and like/dislike buttons. If I hover the cursor in the right place I can see it flash up briefly before fading
Other symptoms include: Messed up 'see reply' results, and the video jumping to the right occasionally.
The only thing I think would do this is ghostery, but that is disabled for youtube.
Buttons are fine in firefox so I think this is isolated to chrome. I've noticed in chrome, on some sites like people personal sites the buttons show, but on my dash they don't.