Button Disappears?

I have a pause button but whenever I run my code it works fine the first time but then it disappears.

Here is code: using System.Collections; using System.Collections.Generic; using UnityEngine; using UnityEngine.SceneManagement;

public class PauseControllerScript : MonoBehaviour {

 public string mainMenu;

 public bool isPaused;

 public GameObject pauseMenuCanvas;

 public GameObject spawner;

 public GameObject cups;

 public GameObject button;



 // Use this for initialization
 void Start () {
     
 }
 
 // Update is called once per frame
 public void Update () {
     if (isPaused) {
         pauseMenuCanvas.SetActive (true);
         Time.timeScale = 0f;
         spawner.GetComponent <BallSpawn> ().enabled = false;
     } else {
         pauseMenuCanvas.SetActive  (false);
         Time.timeScale = 1f;

     }
         

 }

 public void Resume () {
 
     isPaused = false;

 }

 public void Quit () {
     SceneManager.LoadScene ("StartScreen");
 
 }



 public void Yes () {
     isPaused = true;
     button.SetActive (false);
 }

}