After completing the intro sequence and exiting the first room, I got to the three way hallway as usual. I entered one of the doors which lead to a glitched Heavy Containment Entrance. I brought up the Debug HUD and paused via the inventory. The game had an MAV when I brought up the inventory. I suspect there might be an bug in the game's Map System. I took a screenshot below.

EDIT: I still have a save, so I can test this out further. This map seems to be wonked up in other ways as well. Chief Franklin was a Class-D in the "Agent! Behind you!" Scene.

The map seed is 7fwpx0jz.

EDIT EDIT: I managed to get in the room. The Light Containment Entrance leads to nothing. (See second screenshot)

MUDDERFUKIN EDIT: The Heavy Containment Door leads to SCP-372's room. (See screenshot 3)

OH DEAR GOD ANOTHER EDIT: The other room is the unreachable area in the checkpoint.
This is the last update, I swear.

Saw that before. It happens when a room is replaced by a checkpoint most likely a four- or threeway hallway. But I think it was a self created map that had these issues. Rooms were transformed into checkpoints that were also in the wrong angle seen in your first screenshot. But I've no solution for that bug.

I fixed that bug with the BoH mod:

In MapSystem.bb:

Around line 4650, find this: Replace it with: Around line 4670, find this: Replace it with: