It's a blob shadow which is built in Unity's standard asset package.
As you see in the figure below, a shadow that is created by the Unity Projector is duplicated at the floor below.
How can I prevent this duplicated shadow?
YES, you can try with a ray in direction of the shadow that get the altitude or distance and set the maximum shadow projector distance similar to ray result dynamically using physics ray.
Ray ray = new Ray(hit.transform.position, -Vector3.up);
Or you can use Unity shadow only for that particular object.