I just got this problem yesterday (super annoyingly after RENTING a movie on Youtube!), and it seems to have been affecting people with all major browsers and both Windows and Mac.

Just wondering if anyone else here has had this problem and maybe found a solution...

Do you mean the arrow at the bottom of the screen that lets you scroll down to the comments? Yeah,that is a new feature I noticed a little while ago. I use both Opera and Firefox and it's not an issue with either of them. (Win 10)

Looks like it was a problem with Edge though.