The player model reacts strangely to light. Why? How to fix?

Question

Unity

The player reacts very strangely to light. If you look at him from behind, then his left arm and left leg will be darker than the rest of the body, and vice versa, if you look at him from the front, then his left arm and left leg will be lighter than the rest of the body. Why? How to fix?

Answer 1

sounds like inverted normals

Answer 2

The screenshot is not very clear, but it seems like there really are problems with inverted normals. See how to fix them in your software.