Try walking off the elevator platform that pops up under the car lift at Saul's while returning to the resistance HQ as it lowers. When I did, I fell through a hole in map beneath the elevator and stayed alive. I was able to walk around the entire map of Subway Town from underneath, seeing everything above me. It was actually pretty cool. I had to load another save or quit to escape though. See if you can duplicate this glitch and reply here.

Yeah this has happened to me quite a few times.