Weird lighting/shadow with some landscape surfaces?

Hello everyone,

I was trying to make a map using landscape tool, and I came across weird problem. As it can be seen from the image; when I paint the landscape, rocks are bright and shadows on them can be seen but grass is always dark and there is no shadow on it. I’m using starter content textures, and my landscape material only has base colors and normal maps. What can be the problem?

I couldn’t find anything why it is happening. bump