Ue4.12 KiteDemo very dark, why?

Where can I have a strange shadows on the ground, why?

How to Fix?

This looks like material quality issues. Kite demo is meant for really high-end machines and the quality on the textures looks pretty low, especially when you were looking at the grass. The clouds use a light function material, and if the material quality gets lowered this could potentially happening. So with the darkening of the cloud light function material quality that looks like it also made the Eye-Adaptation from the Post Process also kick in to be a bit darker too.