This just started today, but I had the Adblock app on my Ipad for Safari and it has been working without a flaw. All of a sudden today whenever I go to youtube.com to watch a video it pops up with a commercial first, and in the progress bar shows that it has like eight more commercials lined up for me to watch.
I think it might be an issue with Safari because I downloaded TWO more adblockers and have set them up in the content blocker section of Safari in settings. But, still, no amount of configuration or playing with the whitelist stops these intrusive commercials.
Read more: Adblock for Safari on Ipad isn't blocking Youtube ads