its because of the ABT build you build your levels with. the lightning, especially the dynamic lights aswell as the decals are off. the engine basically renders level geometry as polygons now, and sometimes cuts off polys wrongly.
you can try to fix that by setting the WED properties lighting either to ncie dynamic lighting in level build, with small tesselation, remove dynamic light, build as BSP, or check the merge across leafs and chek/uncheck the dont snap vertices flag.
you have to try around a little. this is an error on the engines part and i doubt my tipps help, but its better than nothing...