Why is this strange shadow being created?

Why is this strange shadow being created?

It is caused by these outer surfaces.

When I remove them, there is no shadow at all in the shadow.

I want to keep the shape with the sides as it is. But how can I remove this strange shadow? Why is it not a continuous shadow?

Best regards,
René

Be sure all normals facing correct direction.

All normals facing correct direction.

The problem was, i used multiple Light > Sun. Each sun create his own shadow and i didn´t disabled shadow in the light properties for the others sun´s.