In this image the 3D camera is looking through a gap in a wall, which gives view to a darker 3D room on the other side that is filled with water. The room on the other side of this wall appears darker because a partially transparent black 3D object has been placed between the two rooms, and so looking through it makes the other room appear darker. The black 3D object only has one visible face, the one the player is looking through.
The problem is that this darker room has a ceiling, but for some reason the ceiling is not visible when viewed through the partially transparent black 3D object that makes the room look darker. Even if the black object is set to only 1% opacity - looking through it still causes the entire ceiling to be invisible, leaving only the black skybox above.
This appears to be some kind of technical nuance within the engine itself that I do not understand, some kind of mesh or blending thing or something. Every other surface in the room is visible when looking through the black object, except the ceiling above; which is an elevated Tiled Background.