MouseLook movement diagonal stutters...

Hi, i´m using the original "MouseLook.cs" script from the standard unity package. I added this script to my camera and now i´m´wondering, why the camera movement is stuttering when rotating the mouse diagonal. There´s no fluid movement like rotating only left or only right. Any ideas how to fix that?

  [AddComponentMenu("Camera-Control/Mouse Look")]
     public class MouseLook : MonoBehaviour {
     
         public enum RotationAxes { MouseXAndY = 0, MouseX = 1, MouseY = 2 }
         public RotationAxes axes = RotationAxes.MouseXAndY;
         public float sensitivityX = 15F;
         public float sensitivityY = 15F;
     
         public float minimumX = -360F;
         public float maximumX = 360F;
     
         public float minimumY = -60F;
         public float maximumY = 60F;
     
         float rotationY = 0F;
     
         void Update ()
         {
             if (axes == RotationAxes.MouseXAndY)
             {
                 float rotationX = transform.localEulerAngles.y + Input.GetAxis("Mouse X") * sensitivityX;
                 
                 rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
                 rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);
                 
                 transform.localEulerAngles = new Vector3(-rotationY, rotationX, 0);
             }
             else if (axes == RotationAxes.MouseX)
             {
                 transform.Rotate(0, Input.GetAxis("Mouse X") * sensitivityX, 0);
             }
             else
             {
                 rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
                 rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);
                 
                 transform.localEulerAngles = new Vector3(-rotationY, transform.localEulerAngles.y, 0);
             }
         }
         
         void Start ()
         {
             // Make the rigid body not change rotation
             if (rigidbody)
                 rigidbody.freezeRotation = true;
         }
     }