there really is an invisible barrier that triggers a scene when trying to get to the boss room alone... what order of events occured to let you get there? cause you normally lose the key to the warehouse so you need sylphy to open it
I never met her in my first run. I went in, retrieved the warehouse key, no succubus pair fight happened (IIRC I moved through the lower route between crates I think), I used the key, I navigated the warehouse (also pushed the boxes into place while there) and got to the boss, who I got to and then saw the bad end.