Why cant any operations be performed in camera when loaded from the previous scene?

I have a start scene which has a start button. The start scene has a Camera adaptor gameobject. Camera adaptor gets main camera and performs some operations on every scene. When I click on start and the next scene is loaded, the camera adapter object is available in next scene but the camera and camera is also loaded. But I cannot perform any operations on camera like changing its position, etc. here is my code and configuration: alt text

 public class CameraAdaptor2D : MonoBehaviour
 {
 
     float displayWidth;
     float displayHeight;
 
     [SerializeField] Camera cam;
 
 
     void OnEnable()
     {
         SceneManager.sceneLoaded += OnSceneLoaded;
     }
 
     void OnSceneLoaded(Scene scene, LoadSceneMode mode)
     {
         cam = Camera.main;
     }
 
     // called when the game is terminated
     void OnDisable()
     {
         Debug.Log("OnDisable");
         SceneManager.sceneLoaded -= OnSceneLoaded;
     }
 
     private void Awake()
     {
         DontDestroyOnLoad(this);
     }
 
     void Start()
     {
         displayWidth = Screen.width;
         displayHeight = Screen.height;
 
         PositionCamera();
 
     }
 
     void PositionCamera()
     {
         Vector3 vector = new Vector3(0.0f,0.0f,0.0f);
         cam.transform.position = vector;
     }

In the above code, the camera stays in its position. It does not move. even when I try to debug and add a breakpoint in PositionCamera(), it does not hit that breakpoint. What amI doing wrong here? How can I correct it?