ImageButton is visible only after resize - Libgdx - resize

Question

I have a class called "HudBarView" which takes care of the drawing of the HUD Bar at the top of the screen(Pause button, score, etc).
This class extends the Group class(scene2d).
Another class I have is "HUDManager" which takes care of all the HUD work in the game, including HUD Bar.
Now, currently I have only a pause button in my HUD Bar but the problem is - it is visible only after I resize the screen. Very weird problem.
Here is my HudBarView class:
package views.hud.views;
import views.renderers.HUDManager;
import com.badlogic.gdx.graphics.g2d.TextureAtlas;
import com.badlogic.gdx.scenes.scene2d.Group;
import com.badlogic.gdx.scenes.scene2d.ui.ImageButton;
import com.badlogic.gdx.scenes.scene2d.ui.Skin;
import engine.helpers.AssetsManager;
import engine.helpers.Values;
public class HUDBarView extends Group{
private ImageButton pause;
private HUDManager hud_manager;
private Skin skin;
public HUDBarView(HUDManager hud_manager) {
this.hud_manager = hud_manager;
initiate();
}
private void initiate() {
skin = new Skin(AssetsManager.getAsset(Values.BUTTONS_PACK, TextureAtlas.class));
pause = new ImageButton(skin.getDrawable("pause"));
pause.setSize(Values.Pause_Width, Values.Pause_Height);
pause.setPosition(Values.SCREEN_WIDTH - pause.getWidth(), Values.SCREEN_HEIGHT- pause.getHeight());
addActor(pause);
}
}
Here is my HUDManager class:
package views.renderers;
import views.hud.ParticleEffectsActor;
import views.hud.views.HUDBarView;
import aurelienribon.tweenengine.TweenManager;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.g2d.TextureAtlas;
import com.badlogic.gdx.math.MathUtils;
import com.badlogic.gdx.math.Vector2;
import com.badlogic.gdx.scenes.scene2d.Group;
import com.badlogic.gdx.scenes.scene2d.Stage;
import com.badlogic.gdx.scenes.scene2d.ui.Image;
import com.badlogic.gdx.scenes.scene2d.ui.Label;
import com.badlogic.gdx.scenes.scene2d.ui.Skin;
import engine.helpers.AssetsManager;
import engine.helpers.UIHelper;
import engine.helpers.Values;
public class HUDManager extends Group {
private Stage stage;
private Skin skin;
private Image text;
private HUDBarView hudView;
public HUDManager(Stage stage) {
this.stage = stage;
initiate();
addActor(hudView);
addActor(particles);
}
public void initiate() {
skin = AssetsManager.getAsset(Values.GAME_SKIN_PACK, Skin.class);
hudView = new HUDBarView(this);
particles = new ParticleEffectsActor();
}
public Stage getStage() {
return stage;
}
}
Here are some photos that will help you understand the problem a little bit better:
Before the screen is resized(it doesn't matter how much the screen is resized):
http://i.gyazo.com/5cc675bde2fcbba7492bba69d4a419c6.png
After the screen is resized:
http://i.gyazo.com/d6814f3e15b903d59dab74b83e95292c.png
P.S Here is my render method inside the Game Screen class(I omitted all the irrelevant parts):
public void render(float delta) {
switch(state) {
case RUN:
// if The asset manager is done loading
if(AssetsManager.update() && !doneLoading) {
doneLoading = true;
hudManager = new HUDManager(stage);
stage.addActor(hudManager);
renderer = new GameRenderer(world, camera, batch);
loadingRenderer.dispose();
} else if(doneLoading) {
renderer.render(delta);
stage.draw();
stage.act(delta);
world.update(delta);
manager.update(delta);
}
// Display loading information
else
loadingRenderer.render(AssetsManager.getProgress()*100);
case PAUSE:
break;
}
}
EDIT: After playing a little bit with the code I found out that if I pause and then resume the game it causes the ImageButton to appear on the screen.