From invalid materials, to impossibly-complex displacements and missing geometry, there's so much wrong with your map that it feels like half of the work will have to be redone. To start off with the displacements issue, destroy all of them and then select only those faces that are intended to be seen by the player when creating them again. Since displacements don't seal the map, make sure there's solid geometry behind and/or underneath. Don't create displacements for simple brushwork (such as your Control Point in the middle) that can be achieved with the Clipping Tool (
, Shift+X).