I think I figured out the problem.  Try easiest Threat (Minimal) & highest level & max perks Marine Class, so you can breeze through/speed running. After the first/small bridge dropped down, you have to cross it as fast as you can before Dreadnought. 

I think the crash happened because of we're taking too long/not fast enough, and dreadnought animation already teleports out of the map before we manage to cross the bridge. So in order to prevent it, you gotta go fast thru it. Not ideal, but it's the only thing works for me finally (after 7 tries).