One of the JLayeredPane layers is not showing up

Question

There are a number of similar posts, notably: Java Swing JLayeredPane not showing up and Top layer in JLayeredPane not displaying

But none of them seem to solve my specific problem.

I have the following code:

public class PlayScreen{
private JLayeredPane playScreen;
private Player player;
private JPanel towerButtons;
private JPanel detailPanel;
private JLabel map;
public PlayScreen(Player player){
    this.player = player;
    playScreen = new JLayeredPane();
    playScreen.setLayout(new BorderLayout());
    setTowerButtons();
    playScreen.add(towerButtons, BorderLayout.EAST);
    playScreen.setLayer(towerButtons, 0);        
    setDetailLabels();
    playScreen.add(detailPanel, BorderLayout.WEST);
    playScreen.setLayer(detailPanel, 0);        
    setMap(player.getNextMap());
    playScreen.add(map, BorderLayout.CENTER);
    playScreen.setLayer(map, 0);
    JButton playButton = new JButton("play");
    playScreen.add(playButton, BorderLayout.NORTH);
    playScreen.setLayer(playButton, 0);        
    playButton.addActionListener(new playListener());
    playScreen.setVisible(true);
}

where setTowerButtons(), setDetailLabels() and setMap() methods called in the constructor basically initialize the towerButtons, detailPanel and map fields. When the "play" button is pressed, the following code is called:

public class playListener implements ActionListener{
    public void actionPerformed(ActionEvent e){
        Image image = null;
        try{
            image = ImageIO.read(new File("mob1.bmp"));
        }
        catch (Exception e1){
            System.out.println("image creation failed");
        }
        ImageIcon img = new ImageIcon(image);
        JLabel mob1Button = new JLabel(img);
        System.out.println("hi");            
        playScreen.add(mob1Button, BorderLayout.CENTER);
        playScreen.setLayer(mob1Button, 1);
        mob1Button.setVisible(true);
    }
}  

I know that this is definitely called, because "hi" appears on the output stream.

(The playScreen is a JLayeredPane that is constructed from this:)

public class View {
private JFrame frame;
private Container contentPane;
private Player player;
private LoadScreen loadScreen;
private PlayScreen playScreen;
public View(Player player){
    frame = new JFrame("Display");
    contentPane = frame.getContentPane();
    contentPane.setLayout(new BorderLayout());
    this.player = player;      
    frame.setLocationRelativeTo(null); //puts frame in middle of screen
    frame.pack();
    frame.setVisible(true);
}

public void makeLoadScreen(){
    loadScreen = new LoadScreen();
    contentPane.add(loadScreen.getLoadScreen(), BorderLayout.CENTER);
    frame.pack();
}

public void makePlayScreen(Player player){
    contentPane.remove(loadScreen.getLoadScreen());;
    playScreen = new PlayScreen(player);
    contentPane.add(playScreen.getPlayScreen());
    frame.pack();
}

public class LoadScreen{
    private JPanel loadScreen;
    public LoadScreen(){
        loadScreen = new JPanel();
        JButton play = new JButton("Play");
        JButton load = new JButton("Load");
        loadScreen.setLayout(new GridLayout(2,1,0,0));
        loadScreen.add(play);
        loadScreen.add(load);
        play.addActionListener(new OpenActionListener());
        load.addActionListener(new LoadActionListener());
    }

    public JPanel getLoadScreen(){
        return loadScreen;
    }

    public class OpenActionListener implements ActionListener{
        public void actionPerformed(ActionEvent e){
            makePlayScreen(player);//might not be receiving correct player variable?
        }
    }

    public class LoadActionListener implements ActionListener{
        public void actionPerformed(ActionEvent e){

        }
    }
}

}

public GameManager(){
    player = new Player();
    player.setNextMap("map.bmp");
    //Tower tower = new Tower1();
    //player.addUnlockedTower(tower);
    view = new View(player);
    view.makeLoadScreen();
}

A GameManager Class is created. This creates the loadScreen, which has two buttons, "play" and "load." Clicking on "play" creates the playScreen, which is governed by a separate class.

Sorry for all the code, but I have no idea anymore where it is going wrong, I thought it was to do with not setting the sizes of the playScreen, towerButtons etc, as in the similar post, but that didn't seem to work when I added preferred /min / max sizes.

Currently an image of the map comes up, but the image of the "mob1" does not appear at all, and I would expect it to overlay the map image.