Sooo @TeamYouTube this may be nothing but my 4 year old niece did a button mash on my keyboard (Chrome on PC) while a video I was watching was full screened.
Now when I bring up any video there's no video information or comment field.
I can see comments and reply to them.
halp
Aaaaand fixed by clearing the cache. Phew! Though now I'm reeeally curious as to what combination of buttons she pressed to get the "result".