Ray Traced Distance Field Soft Shadows artifact problem

I have an artifacting problem with the Ray Traced Distance Field Soft Shadows and I don’t know what is happening, here is a video showing the problem, link text their seams to be patches of pure black. I also have a problem of the light from my sun directional light coming through the map when it is below the terrain, these issues only seam to happen on the static meshes with sub surface scattering materials.