What is the next step in the "Blow Up the Dam" mission?

So you've cleared off the top of the dam and gone over the barricade? If you go along a little way the paths will split off, one will slope up on the left-hand side and the right-hand side will continue along flat. If you go along the right-hand side there is a lift that will take you to the bottom of the dam to place the charges.

See this video from around the 15:00 minute mark.

I think it's a bug. I had the same issue where the game wouldn't advance. It could be because I ran ahead and killed the enemies on the scaffolding from behind. I tried jumping the gap onto the ladder and fell, but when it restarted from the checkpoint my team then prompted me to jump across. It took a few goes for it to jump without falling (it wouldn't grab the ladder for some reason) but then the game did advance.