Lighting from static meshes not working

Hello, I have made a set of static meshes, none of them have back faces, however the window piece`s is buggy on the lighting being built, I have added a two sided to the material but it still appeared quite buggy. the first image is after lighting is built and the second is during, obviously I want the during effect but you i dont know why this is doing this.

The result you get heavily depends on lightmap resolution of the object, which is receiving your fence shadow. Increase lightmap resolution for the floor piece.