Can't enable/disable canvas on Android device

I'm trying to create a pause menu. When I press the escape button (back button on Android device) the canvas with menu should activate. When I do this on PC in Unity 5 - it works great. When I build and run this app on my Android phone - it doesn't works. I've tried two methods. The first one is:

 public class GameController : MonoBehaviour
 {
     private Canvas pauseMenu;
     private void Start()
     {
         GameObject pauseMenuobject = GameObject.FindWithTag("PauseMenu");
         if (pauseMenuobject != null)
             pauseMenu = pauseMenuobject.GetComponent<Canvas>();
         if (pauseMenuobject == null)
             Debug.Log("Cannot find Canvas");
         pauseMenu.gameObject.SetActive(false);
     }
     void Update()
     {
         if (Input.GetKeyDown(KeyCode.Escape))
             if (!pauseMenu.gameObject.activeInHierarchy)
                 pauseMenu.gameObject.SetActive(true);
             else if (pauseMenu.gameObject.activeInHierarchy)
                 pauseMenu.gameObject.SetActive(false);
     }
 }

And the other one is:

 public class GameController : MonoBehaviour
 {
     private Canvas pauseMenu;
     private void Start()
     {
         GameObject pauseMenuobject = GameObject.FindWithTag("PauseMenu");
         if (pauseMenuobject != null)
             pauseMenu = pauseMenuobject.GetComponent<Canvas>();
         if (pauseMenuobject == null)
             Debug.Log("Cannot find Canvas");
         pauseMenu.enabled = false;
     }
     void Update()
     {
         if (Input.GetKeyDown(KeyCode.Escape)){
             if (pauseMenu.enabled == false)
                 pauseMenu.enabled = true;
             else if (pauseMenu.enabled == true)
                 pauseMenu.enabled = false;
     }
 }

Both work in the Unity 5, but when I build and run it on Android - it doesn't works. Even more, on android it doesn't even disables the canvas in void Start() nor it passes the if () in the void Update().

What am I doing wrong? Is this type of disabling/enabling works only in Unity 5 and does not works when you build it? Or is it because I launch it on the Android? What should I do? Thanks in advance.