Character dark on face

Hello,
today I have a new issue with my game…
This time it is about my player character.
When the sun is at noon (so far above is head), dark things appear on the face of the character… It is quite ugly and I don’t know how to delete that…

Here is a picture :

As you can see, they are dark things arround mouth, eyes and nose.

I first thought that it was due to shadows of the head… So I disable cast shadow to be sure and it doesn’t change anything (just delete the shadow of head on the neck so not interesting).
Then I look at textures etc… nothing was strange, and then I look on my material. I have a param to increase the normal map intensity, so I see that the problem if I increase it.
If I decrease it (to 0, so it is like not having normal), then this strange dark things on face almost disappear, but face is ugly due to not having normal…

Here are two pictures, one when I have not in front of the sun, and the second in the editor when opening the mesh. As you can see it looks totally different…


Have you any idea of why it is acting like this ? Thank you a lot for your time and your help !

All the best