Reloading a Scene throws NullReferenceException on GO with nested Prefabs

I'm doing a simple AR app in which the user has a menu with lamps. By swiping he/she switches lamps game objects (from prefabs) that are all nested on an empty game object. I have a Swipe Detector game object with an event listener which, with an Index, tracks the current active lamp and shows/hides the other as the user swipes (by setting the scale to 0). Then user presses a button that launches an AR Scene to place the lamp on the world. The AR scene has a "Back" button that reloads the menu to start over (by SceneManager.LoadScene("SceneName") method).

However, when I relaunch the menu scene, the swiping does not work anymore, and I get a NullReferenceException on a method I use to get the currently active Game Object. It's driving me nuts... The empty game object with the nested lamps still has n children so I assume the prefab game objects are still there... I'm lost!!! Many thanks to anybody who can help, here's the code (script attached to empty parent GameObject):

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class ItemSwitcher : MonoBehaviour
 {
     public GameObject itemHolder;
 
     public float rotationSpeed = 10f;
     int m_Index;
     int m_Length;
     // Start is called before the first frame update
     void Start()
     {
         itemHolder = GameObject.Find("Item Holder");
         m_Index = 0;
         m_Length = itemHolder.transform.childCount;
 
         Debug.Log("Start(): Current Index " + m_Index.ToString());
         Debug.Log("Start(): Current Length " + m_Length.ToString());
         ResetAllChildren();
         if (!ApplicationModel.configured)
         {
             SwipeDetector.OnSwipe += SwipeDetector_OnSwipe;
             ApplicationModel.configured = true;
             Debug.Log("Start(): Configured!");
         }
     }
 
     // Update is called once per frame
     void Update()
     {
         // rotate holder (and children)
         itemHolder.transform.Rotate(0, rotationSpeed * Time.deltaTime, 0, Space.Self);
 
     }
 
     private void SwipeDetector_OnSwipe(SwipeData data)
     {
         Debug.Log("OnSwipe(): Changing Lamp");
         if (data.Direction == SwipeDirection.Right)
         {
             UpdateChildrenDisplay(true);
         }
         else if (data.Direction == SwipeDirection.Left)
         {
             UpdateChildrenDisplay(false);
         }
     }
 
    
     GameObject GetActiveObject()
     {
         Debug.Log("Getting Child " + m_Index.ToString());
         return itemHolder.transform.GetChild(m_Index).gameObject;
     }
 
     void ResetAllChildren()
     {
         // Leave the first visible
         //itemHolder.transform.GetChild(0).gameObject.GetComponentInChildren<MeshRenderer>().enabled = true;
         itemHolder.transform.GetChild(0).gameObject.transform.localScale = new Vector3(1, 1, 1);
         // Hide all others
         for (int i = 1; i < m_Length; i++)
         {
             //itemHolder.transform.GetChild(i).gameObject.GetComponentInChildren<MeshRenderer>().enabled = false;
             itemHolder.transform.GetChild(i).gameObject.transform.localScale = new Vector3(0, 0, 0);
         }
     }
     void UpdateChildrenDisplay(bool right)
     {
 
         //GetActiveObject().GetComponentInChildren<MeshRenderer>().enabled = false;
         GetActiveObject().transform.localScale = new Vector3(0, 0, 0);
         if (right)
         {
             m_Index++;
             m_Index = m_Index % m_Length;
         }
         else
         {
             m_Index--;
             m_Index = m_Index == -1 ? m_Length - 1 : m_Index;
         }
         GameObject go = GetActiveObject();
         //go.GetComponentInChildren<MeshRenderer>().enabled = true;
         go.transform.localScale = new Vector3(1, 1, 1);
         // This is not very good but...
         // Index should match prefab name - 1 (so Lamp1 has index 0)
         ApplicationModel.currentObject = (m_Index + 1).ToString();
         Debug.Log("OnSwipe(): Current Lamp is Lamp" + (m_Index + 1).ToString());
     }
 }