If you are using the Adblock Plus extension on a desktop browser, you should not be seeing full length ads though you may see a variety of different behaviors such as a temporary black screen or a very brief display of an ad (less than a second or two).
These are related to our efforts to stop the entirety of the ad appearing. If you are seeing full length ads, I recommend checking out this article: https://help.adblockplus.org/hc/en-us/articles/26653087560595-Ads-appearing-on-YouTube
