Hello,
I try Eevee for the first time, but I don’t understand some behaviour.
I do a very simple object, with very simple material and a very simple lighting, and I have a “hole” in my shadow :
It’s hard to say, I don’t really know what your object looks like nor what your lighting setup is 
A wireframe render would be helpful, as well as a viewport showing the light angle.
That aside… have you checked face orientation? Viewport Overlays >. Face Orientation, anything red needs Mesh > normals > flip
You are right, that was a face orientation problem. My object is a curved plane so there is always some face that are badly oriented. I have added a “solidify” modifier and that solve my problem.
