Custom editor does not work well after Play

I want to create a grid editor and I have two parts: GridManager, GridEditor

Beginning the custom editor works well, but after Playing I got a problem. The Unity editor couldn't repaint scene view when modify the grid properties in the Inspector panel.

Beginning the editor was well (would repaint scene view)

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After playing, happened the problem (would not repaint)

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GridManager.cs

 [ExecuteInEditMode]
 public class GridManager : MonoBehaviour
 {
     private static GridManager Instance = null;
 
     public static GridManager instance
     {
         get
         {
             if(Instance = null)
             {
                 Instance = FindObjectOfType(typeof(GridManager)) as GridManager;
 
                 if (Instance == null)
                 {
                     Debug.LogError("Could not find the GridManager script");
                 }
             }
 
             return Instance;
         }
     }
 
     
     public int numOfColumns;
     public int numOfRows;
     public float gridCellSize;
 
     private Vector3 origin = new Vector3();
     public Vector3 Origin { get { return origin; } }
     public Node[,] nodes { get; set; }
     public List<int> obstacles = new List<int>();
 
 
     void Awake()
     {
         Initialize();
     }
 
     void Update()
     {
         origin = transform.position;
     }
 
     void Initialize()
     {
         // declare nodes
     }
 }

GridEditor.cs

 using UnityEngine;
 using UnityEditor;
 using System.Collections;
 using System.Collections.Generic;
 
 [CustomEditor(typeof(GridManager))]
 public class GridEditor : Editor {
 
     GridManager grid;
 
     static bool showGrid;
     static bool showGridLabel;
     static bool showObstacles;
     static int labelSize;
 
     static Color gridColor = Color.white;
     static Color obstacleColor = new Color(0.5f, 0.0f, 0.0f, 0.25f);
     static Color labelColor = Color.green;
     static Color coordinateColor = Color.cyan;
 
     public void OnEnable()
     {
         grid = target as GridManager;
 
         if (SceneView.onSceneGUIDelegate == null)
         {
             SceneView.onSceneGUIDelegate += OnScene;
         }
     }
 
     public void OnDestory()
     {
         SceneView.onSceneGUIDelegate -= OnScene;
     }
 
     public override void OnInspectorGUI()
     {
         DrawDefaultInspector();
 
         EditorGUILayout.Space();
         EditorGUILayout.BeginHorizontal();
         showGrid = EditorGUILayout.Toggle("Show Grid", showGrid);
         gridColor = EditorGUILayout.ColorField(gridColor);
         EditorGUILayout.EndHorizontal();
         EditorGUILayout.BeginHorizontal();
         showGridLabel = EditorGUILayout.Toggle("Show Grid Label", showGridLabel);
         labelColor = EditorGUILayout.ColorField(labelColor);
         coordinateColor = EditorGUILayout.ColorField(coordinateColor);
         EditorGUILayout.EndHorizontal();
         EditorGUILayout.BeginHorizontal();
         showObstacles = EditorGUILayout.Toggle("Show Obstacles", showObstacles);
         obstacleColor = EditorGUILayout.ColorField(obstacleColor);
         EditorGUILayout.EndHorizontal();
         labelSize = EditorGUILayout.IntSlider("Label Size", labelSize, 0, 50);
 
         EditorGUILayout.Space();
         if (GUILayout.Button("Clear Obstacles", GUILayout.Height(30)))
         {
             grid.ClearObstacles();
         }
 
         EditorGUILayout.Space();
         EditorGUILayout.HelpBox("When enable the 'Show Obstacle' toggle \nPress key 'A' to add or remove the obstacle",
             MessageType.None, true);
 
 
         if (GUI.changed)
         {
             EditorUtility.SetDirty(target);
         }
 
         SceneView.RepaintAll();
     }
 
     void OnScene(SceneView sceneview)
     {
         if (showGrid)
         {
             DrawGrid();
         }
 
         if (showObstacles)
         {
             ObstacleEditor(Event.current);
 
             DrawObstacles();
         }
     }
 
     void DrawGrid()
     {
         int columns = grid.numOfColumns;
         int rows = grid.numOfRows;
         float cellSize = grid.gridCellSize;
         Vector3 origin = grid.Origin;
         Handles.color = gridColor;
 
         if (columns > 0 || rows > 0 || cellSize > 0)
         {
             float width = columns * cellSize;
             float height = rows * cellSize;
 
             // draw the horizontal lines
             for (int i = 0; i < rows + 1; i++)
             {
                 Vector3 startPos = origin + i * cellSize * new Vector3(0.0f, 0.0f, -1.0f);
                 Vector3 endPos = startPos + width * new Vector3(1.0f, 0.0f, 0.0f);
                 Handles.DrawLine(startPos, endPos);
             }
             // draw the vertical lines
             for (int i = 0; i < columns + 1; i++)
             {
                 Vector3 startPos = origin + i * cellSize * new Vector3(1.0f, 0.0f, 0.0f);
                 Vector3 endPos = startPos + height * new Vector3(0.0f, 0.0f, -1.0f);
                 Handles.DrawLine(startPos, endPos);
             }
 
             // draw the gird labels
             if (showGridLabel)
             {
                 int index = 0;
                 float posOffset = cellSize * 0.25f;
                 GUIStyle guistyle = new GUIStyle();
                 guistyle.normal.textColor = labelColor;
                 guistyle.fontSize = labelSize;
 
                 // draw the cell index
                 for (int i = 0; i < rows; i++)
                 {
                     for (int j = 0; j < columns; j++)
                     {
                         float xPos = j * cellSize + posOffset;
                         float zPos = i * (-cellSize) - posOffset;
                         Vector3 labelPos = origin + new Vector3(xPos, origin.y, zPos);
                         Handles.Label(labelPos, index.ToString(), guistyle);
                         index++;
                     }
                 }
 
                 // draw the row and column label
                 guistyle.normal.textColor = coordinateColor;
 
                 for (int i = 0; i < rows; i++)
                 {
                     float xPos = (-cellSize) + posOffset;
                     float zPos = i * (-cellSize) - posOffset;
                     Vector3 labelPos = origin + new Vector3(xPos, origin.y, zPos);
                     Handles.Label(labelPos, i.ToString(), guistyle);
                 }
 
                 for (int i = 0; i < columns; i++)
                 {
                     float xPos = i * cellSize + posOffset;
                     float zPos = cellSize - posOffset;
                     Vector3 labelPos = origin + new Vector3(xPos, origin.y, zPos);
                     Handles.Label(labelPos, i.ToString(), guistyle);
                 }
             }
         }
     }
 
     void ObstacleEditor(Event e)
     {
         float cellSize = grid.gridCellSize;
 
         if (e.type == EventType.KeyUp && e.keyCode == KeyCode.A)
         {
             Ray r = Camera.current.ScreenPointToRay(new Vector3(e.mousePosition.x, -e.mousePosition.y + Camera.current.pixelHeight));
 
             Vector3 cellPos = new Vector3(
                 Mathf.Floor(r.origin.x / cellSize) * cellSize + cellSize * 0.5f,
                 grid.Origin.y,
                 Mathf.Floor(r.origin.z / cellSize) * cellSize + cellSize * 0.5f);
 
             int index = grid.GetGridIndex(cellPos);
             MarkObstacle(index);
         }
     }
 
     void MarkObstacle(int index)
     {
         if (!grid.AddObstacle(index))
         {
             grid.RemoveObstacle(index);
         }
     }
 
     void DrawObstacles()
     {
         int columns = grid.numOfColumns;
         int rows = grid.numOfRows;
         float cellSize = grid.gridCellSize;
         List<int> list = grid.obstacles;
 
         if (columns > 0 && rows > 0 && cellSize > 0 && list != null)
         {
             foreach (int index in list)
             {
                 Vector3 v = grid.GetGridCellCenter(grid.GetGridCoordinate(index));
                 Vector3[] verts = new Vector3[] {
                 v + new Vector3(-cellSize*0.5f, 0.0f, +cellSize*0.5f),
                 v + new Vector3(cellSize*0.5f, 0.0f, +cellSize*0.5f),
                 v + new Vector3(cellSize*0.5f, 0.0f, -cellSize*0.5f),
                 v + new Vector3(-cellSize*0.5f, 0.0f, -cellSize*0.5f)
             };
 
                 Handles.DrawSolidRectangleWithOutline(verts, obstacleColor, obstacleColor);
             }
         }
     }
 }
 

What happened about this ?