Hi Reload,
This looks like you have the light too low in this area and the with direct capsule shadows enabled. As the actor crosses the light the geometry of the mesh is crossing the point where the light is placed and thus you’ll get this shadowing on both sides. If you moved the light up higher you’ll see this issue go away.
Given that you’ve not posted details about where the light is physically placed or any settings you’ve used for the light or character, I have to infer some things, but this is my best guess with what you’re seeing here.
-Tim