Scene loading issue in Unity 5.3?

Question

Unity

I am making a game on Unity 5.3. There are two scenes - the scene with the game itself and the scene with the main menu. When loading in the scene editor with the game directly, everything is fine - all animations and controls work. But if I first load the scene with the menu, and through the playtest I load the scene with the game, then the picture freezes there, everything is static and lifeless, until I stop the playtest. I load the scene through LoadScene by pressing the button. Again, when loading the scene with the game directly, it works fine.
The code:

using UnityEngine;
using System.Collections;
using UnityEngine.SceneManagement;

public class MainMenuScript : MonoBehaviour {

  public void PlayPressed () {
    SceneManager.LoadScene ("MainLevel");
  }	
  public void ExitPressed () {
    Debug.Log("Exit");
    Application.Quit();

  }

}