Continue blocks - Complete All blocks above

Hello

Can someone explain exactly how the Continue block - 'Complete All Blocks Above' works?

I have a lesson that's comprised of one video, a couple of gifs, some audio files, a button, and some still images along with explanatory text. This is followed by a Continue block set to 'complete all blocks above'. Logically I would think that viewing the video is the element that would unlock the Continue button. It does not. I can't figure out what other element is preventing it from unlocking it.

I have other lessons that comprise of the same elements and only viewing the video unlocks the Continue block. 

Thanks, Marion