If you increase the size of the Sky Sphere, there is a second sun as the time from which the shadows fall! help how to fix it? 
If you’re using BP_SkySphere you need to call a function on it called Update Sun Direction. To do this just make a reference to your BP_SkySphere and call that function on a blueprint. Or if your sun is not dynamic, you could just refresh its material by ticking Refresh Material checkbox in BP_SkySphere’s details panel.
To Refresh Material check is not put