Sadly, on mobile (youtube app, ios) once the ad comes up you are locked in, and the next/previous buttons go away. I was watching on mobile the other day and accidentally clicked either next or previous. Got immediately sucked into an ad, and had to wait several seconds before returning to the content i actually wanted to watch.

most of the time i try to use the web-view instead of the app. i see way less (or maybe zero?) ads there.