So youtube has been trying to restrcit users with adblockers enabled on the site for a while now. Most notably people using uBlockOrigin, or uBO. There is an ongoing battle between uBO devs and the youtube anti-adblock script.
However, I want to point out that you can always just block the popup window using the element picker from uBO. Of course a lot of people realized this, but the flaw of this method is that you can't scroll as it's disabled as part of the popup window script. There is an easy fix to this: just enter and exit fullscreen, voila problem solved. You can even write a script that does this automatically upon opening a youtube page.

#youtube #uBlockOrgin #adblocker