hi, welcome to the forum :) it's a known bug (should have been fixed with the last patch, didn't work apparently) according to at least this german thread you should be able to walk though the passage and continue the quest :) (just beware of invisible enemies) Just tried this and it totally worked...

i am currently trying to finish the quest "long way to the top", and have run into an issue. after going through old arch and getting to the long tunnel with all of the tubes you drop down onto, i get to the bottom and see this (attached photo, sorry its not a screen shot wasnt able to get that to w...