shadow problem with a shdaer

Hello everyone.

I am having a problem with a shader that I am using.

It is a problem with shadows, sometimes, depending on the angle of the light source, it displays the shadows badly in some places. see my pictures below and i dont understand why.

it doesn't matter if the angle of the light source changes or remains fixed.


do you have any idea about this problem?

Thank you in advance.

Laurent