Lighting error on procedural mesh


I’m currently trying to make procedural terrain in UE4. I’m having an issue however with light bleeding from the edges of the mesh if the directional light moves behind it. I have tried using a two sided material and generating back facing pollys but to no success. Any Ideas why this may be happening? Both the directional light and skylight are movable.

Thank you for your help

You either need something on the bottom to block the light (not just complete cubes) or you need to try to adjust the shadow bias setting for the light, however that will likely give some shadow artifacts so it would be better to place something to block the light.