I can see the same map at 0:25 of this video. You mean the passage at 0:32?
The one to the left of the train you leave at the start of mission 12 that leads to some stairs?
I took a fast look at multiple walkthroughs and its always meant to be open. I suppose the door you are seeing doesn't show the option to either use the hacking tool or the torch. Is it just a blank wall? Might be bugged or something.
Are you playing on steam? Can try to verify integrity of game files, reintall game(saved games are in cloud so you shouldn't lose progress). You can also use mission select and reload mission 12, might replace your current bugged save with a good one.