This happened a couple of times trying today's sortie. I got vaguely near vault A in the new Gas City Spy mission, but I was still 100m or so away, before I even got to the initial panel that opens up the room, the alarms for A triggered. I was solo, so no one else was messing with it either.
(I'm a little extra bitter about it, because I finally got Repair Kit to drop during one of them.)