Tilemap - How to merge more tilemaps into one array

I'm making a 2D RPG game in Unity. I need a room detection... so I would like to get all tiles from more tilemaps and merge them into one array in the script. I have a problem, because not all tiles are imported. For example it imports 11 door instead of 30.

My C# code:

 public class RoomController : MonoBehaviour{
 public Tilemap floor;
 public Tilemap walls;
 public Tilemap doors;
 public WorldGraph worldGraph;
 public List<Room> rooms;
 Queue<ClonedTile> queue;
 // Start is called before the first frame update
 void Start()
 {
     rooms = new List<Room>();
     rooms.Add( new Room() );
     UnityEngine.Debug.Log( "Rooms: " + rooms.Count );
     worldGraph = new WorldGraph(walls.cellBounds.size.x, walls.cellBounds.size.y, walls, floor, doors, this);
 }

This is my worldGraph class:

 public class WorldGraph {
 public ClonedTile[,] tiles;
 Tilemap walls;
 Tilemap floor;
 Tilemap door;
 Dictionary<ClonedTile, TileBase> originalTiles;
 public int width;
 public int height;
 RoomController roomController;

 public WorldGraph(int width, int height, Tilemap walls, Tilemap floor, Tilemap door, RoomController roomController ) {
     tiles = new ClonedTile[width, height];
     this.walls = walls;
     this.floor = floor;
     this.door = door;
     this.width = width;
     this.height = height;
     this.roomController = roomController;

     Debug.Log( width + " " + height );
     originalTiles = new Dictionary<ClonedTile, TileBase>();

     ImportTiles();
 // This is the place, where I import all tiles.

 public void ImportTiles() {
     for(int y = 0; y<height; y++ ) {
         for(int x = 0; x<width; x++ ) {
             Vector3Int pos = new Vector3Int( x, y, 0 );

             TileBase tile = floor.GetTile(pos);

             if(tile!= null ) {
                 tiles[x, y] = new ClonedTile( x, y, TileType.Floor, false );
             }

             if(tile == null ) {
                 tiles[x, y] = new ClonedTile( x, y, TileType.Empty, false );
             }

             tile = walls.GetTile( pos );
             if (tile != null ) { 
                 tiles[x, y] = new ClonedTile( x, y, TileType.Wall, true );
             }

             tile = door.GetTile( pos );
             if(tile!= null ) {
                 tiles[x, y] = new ClonedTile( x, y, TileType.Door, true );
             }
         }
     }

     int wallnumber = 0;
     int floornumber = 0;
     int doornumber = 0;
     int emptynumber = 0;
     foreach (ClonedTile t in tiles ) {

         t.roomController = roomController;
         roomController.GetOutsideRoom().Tiles.Add( t );
         t.hasRoom = false;



         switch ( t.type ) {
             case TileType.Wall:
                 wallnumber++;
                 break;
             case TileType.Door:
                 doornumber++;
                 break;
             case TileType.Floor:
                 floornumber++;
                 break;
             default:
                 emptynumber++;
                 break;
         }
     }
     Debug.Log( "Walls: " + wallnumber + " Floor: " + floornumber + " Doors: " + doornumber + " Empty: " + emptynumber );
 }

}

I would be glad for any suggestions.