[Solved] Custom editor resets after Play?

Hello all,

Asking for your help and guidance on this one.

I am making a custom editor to instantiate and destroy multiple objects using two GUI buttons. In edit mode, all is working fine, I can instantiate multiple prefabs, and then destroy them, one by one, from last instantiated to first, but as soon as I press "Play" and the "Stop", I am not able to destroy any previously instantiated prefabs (instantiated before play-mode). I can instantiate new prefabs and then destroy them, but as for those prefabs that were instantiated before I hit play - they stay unaffected.

Now, I am not that much worried that this happens in play mode, but I definitely want to continue from the point before play mode.

Whenever a prefab is instantiated, I add it to a Stack and keep a track of the size. After I hit play - stop, it seems to reset to 0.

After browsing numerous posts about a similar problem and checking Unity's API, I do realize I need to figure out a way to save the custom editor settings and variables by serializing them or making them dirty, I just do not know how to accomplish this. I've tried what was suggested in those posts, but nothing seems to be working in my case (or I'm doing something wrong).

I have a Monobehaviour script and an Editor script. I'll post the snippets for a single type of the object, as other parts are the same.

Here is the first one:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 [System.Serializable, ExecuteInEditMode]
 public class ObjectControl: MonoBehaviour {
 
     [SerializeField, HideInInspector]
     public Stack<GameObject> undoStack = new Stack<GameObject>();
     public GameObject instance;
     public int undoStackSize;
     public int objectSelectionIndex = 0;
     
     public void placeObject()
     {
         switch (objectSelectionIndex)
         {
             case 1:
 
                 Debug.Log("Just received a number 1 from the editor");
                 GameObject object_A = Resources.Load("Prefabs/Object_A") as GameObject;
                 instance = Instantiate(object_A, this.transform.position, this.transform.rotation, this.transform);
                              
                 undoStack.Push(instance);
                 undoStackSize = undoStack.Count;
 
                 break;
  
             case 4:
 
                 Debug.Log("Just received a number 4 from the editor, deleting the object");
 
                 if (undoStack.Count > 0)
                 {
                     GameObject objToUndo = undoStack.Pop();
                     DestroyImmediate(objToUndo);
                     undoStackSize--;
                     
                 }
 
                 else
                 {
                     Debug.Log("Stack is empty! Stack size is: " + undoStack.Count);
                 }
 
                 break;
         }
     }

And the Editor script:

 using UnityEngine;
 using System.Collections;
 using UnityEditor;
 using System.Collections.Generic;
 
 
 [CustomEditor(typeof(ObjectControl)), CanEditMultipleObjects]
 public class ObjectControlEditor : Editor
 {
    
     int objectSelectionToolbar = 0;
     int numberOfPossibleUndo;
         
     bool chooseOption = false;
     bool objectSelectionFoldout = false;
       
     public ObjectControl scriptTarget;
 
     public void Awake()
     {
         scriptTarget = (ObjectControl)target;
     }
 
     public override void OnInspectorGUI()
     {
         DrawDefaultInspector();
 
         GUI.changed = false;
 
         chooseOption = EditorGUILayout.Foldout(chooseOption, "Choose a segment to add:");
 
         if (chooseOption)
         {
 
             EditorGUILayout.BeginVertical();
 
             stationSelectionFoldout = GUILayout.Toggle(stationSelectionFoldout, "" + (stationSelectionFoldout ? "▼ Object selection ▼" : "► Object selection ◄"), "Button", GUILayout.MaxWidth(Screen.width), GUILayout.Height(25));
 
             if (objectSelectionFoldout)
             {
                     
                 GUILayout.Space(5);     //Space before a text box
                 GUILayout.Box("Select lenght of the station:");
                 GUILayout.Space(5);     //Space after a text box and before a toolbox
 
                 string[] objectSelectionToolbarOptions = new string[] { "Object A", "Object B", "Object C" };
 
                 stationSelectionToolbar = GUILayout.Toolbar(objectSelectionToolbar, objectSelectionToolbarOptions, GUILayout.MinWidth(Screen.width), GUILayout.Height(50));
                 GUILayout.Space(5);
 
                 RollerCoasterBuilder scriptTarget = (RollerCoasterBuilder)target;
                 numberOfPossibleUndo = scriptTarget.undoStackSize;
                 
                 switch (objectSelectionToolbar)
                 {
                     case 0:
 
                         GUILayout.BeginHorizontal();
                            
                         if (GUILayout.Button("Place selected object", GUILayout.Height(30)))
                         {
                             scriptTarget.objectSelectionIndex = 1;
                             scriptTarget.PlaceObject();
                         }
 
                         GUILayout.Space(5);
 
                         if (GUILayout.Button("Undo" + "(" + numberOfPossibleUndo + ")", GUILayout.Height(30)))
                         {
                             scriptTarget.objectSelectionIndex = 4;
                             scriptTarget.PlaceObject();
                         }
                                           
                         GUILayout.EndHorizontal();
 
                         break;
                     }
                }  
          }
       if (GUI.changed)
          {
          EditorUtility.SetDirty(target);
          }

}

Any ideas or suggestions are welcome. Thanks in advance ;)