The transition to Sanctuary Gate Road from Northern Narrows can be closed and it automatically locks. Circling around and coming back reveals the entrance into Northern Narrows is still open from the other side, but going back inside opens the transition again even though it was locked before.

The cave entrance on the other side cannot be closed, and thus not be locked. Also, the door cannot be opened from the inside anymore when it has been closed so I was wondering if this was intentional at all?

Yes it's unpickable once you close it. Nice way to trap people.

Fixed.