NullReferenceException: Object reference not set to an instance of an object WanderBehavior.LateUpdate

How to solved this for my soldier at Assets/AIScripts/WanderBehavior.cs:71)

void LateUpdate()

    {

        transform.position = new Vector3(transform.position.x, Terrain.activeTerrain.SampleHeight(transform.position), transform.position.z);

    }

}

add a debug to your code, like this:

void LateUpdate() {
    Debug.Log("Active Terrain: " + Terrain.activeTerrain);
    transform.position = new Vector3(transform.position.x, Terrain.activeTerrain.SampleHeight(transform.position), transform.position.z);
}

By doing this you’ll see in the console output that Terrain.activeTerrain has no value, you have to set it.