shadow problem

In the screenshot below you can see tiny waves on the floor from the shadow settings of my directional light (atmosphere sun light).
How can I eliminate this ?
Of course I played around with the settings and the build lighting quality.

Those are dynamic shadows, the effect becomes more apparent when the light becomes closer to parallel with the surface

edit shadow bias in light details panel, this glitch affects only dynamic shadow ^ like said above, so you wont see them after build when using stationary or static light