Memory leak

Greetings, I have a script for displaying rewarding ads that hangs on the prefab button. This button is located on two different panels in each stage. On the Android device, only the end of the advertisement starts to appear after ten scenes and the player is not rewarded, and after twenty scenes the game is interrupted, therefore that there is a memory leak.link text

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using GoogleMobileAds.Api;
 using UnityEngine.Monetization;
 using System;
 
 public class MineBtn : MonoBehaviour
 {
     public int valueOfButton = 5;
     public bool admob = true;
     private FieldFillingManager ffm;
     private double amount = 0;
     private int countUpdate = 0;
 
 # if UNITY_ANDROID
     private const string ad_reward_diamonds = "ca-app-pub-9578413026007667/3802113406";
     private const string ad_reward_filedPanel = "ca-app-pub-9578413026007667/8330371577";
     private const string test_adID = "ca-app-pub-3940256099942544/5224354917";
     private string admob_ID;
     private RewardedAd rewardedAdDiamonds;
     private RewardedAd rewardedAdFiled;
 
 #endif
 
     // Use this for initialization
     void Start()
     {       
         GetComponentInChildren<Text>().text = "+" + valueOfButton.ToString();
         ffm = FindObjectOfType<FieldFillingManager>();
 #if UNITY_ANDROID       
 
         if (admob)
         {
 //            MobileAds.Initialize("ca-app-pub-9578413026007667~1116240310");  перенес в FieldFillingManager
             if (GetComponentInParent<FailedPanel>())
             {
                 admob_ID = ad_reward_filedPanel;
                 this.rewardedAdFiled = CreateAndLoadRewardedAd(test_adID);//ad_reward_filedPanel);
             }
             else
             {
                 admob_ID = ad_reward_diamonds;
                 this.rewardedAdDiamonds = CreateAndLoadRewardedAd(test_adID);// ad_reward_diamonds);
             }
             //           admob_ID = test_adID;
         }
 #endif
     }
 
     public RewardedAd CreateAndLoadRewardedAd(string adUnitId)
     {
         RewardedAd rewardedAd = new RewardedAd(adUnitId);
 
         rewardedAd.OnAdLoaded += HandleRewardedAdLoaded;
         rewardedAd.OnAdFailedToLoad += HandleRewardedAdFailedToLoad;
         rewardedAd.OnAdOpening += HandleRewardedAdOpening;
         rewardedAd.OnAdFailedToShow += HandleRewardedAdFailedToShow;
         rewardedAd.OnUserEarnedReward += HandleUserEarnedReward;
         rewardedAd.OnAdClosed += HandleRewardedAdClosed;
 
         
        // AdRequest request = new AdRequest.Builder().AddTestDevice(AdRequest.TestDeviceSimulator).AddTestDevice("E2940A62C1B655BA").Build();
        // AdRequest request = new AdRequest.Builder().AddTestDevice("E2940A62C1B655BA").Build();
        AdRequest request = new AdRequest.Builder().Build();
 
         
         rewardedAd.LoadAd(request);   
         return rewardedAd;
     }
 
     public void ButtonClick()
     {
         
 #if UNITY_ANDROID
         
         if (admob)
         {
             if (GetComponentInParent<FailedPanel>())
             {
                 if (rewardedAdFiled.IsLoaded())
                 {
                     rewardedAdFiled.Show();
                 }
             }
             else
             {
                 if (rewardedAdDiamonds.IsLoaded())
                 {
                     rewardedAdDiamonds.Show();
                 }
             }
         }
 
 #endif
     }
 #if UNITY_ANDROID
 
 
     public void HandleRewardedAdLoaded(object sender, EventArgs args)
     {
         Debug.Log("HandleRewardedAdLoaded event received ");
         
     }
 
     public void HandleRewardedAdFailedToLoad(object sender, AdErrorEventArgs args)
     {
         Debug.Log("HandleRewardedAdFailedToLoad event received with message: " + args.Message);        
     }
 
     public void HandleRewardedAdOpening(object sender, EventArgs args)
     {
         Debug.Log("HandleRewardedAdOpening event received ");        
 
     }
 
     public void HandleRewardedAdFailedToShow(object sender, AdErrorEventArgs args)
     {     
         Debug.Log("HandleRewardedAdFailedToShow event received with message: "
                              + args.Message);
     }
 
     public void HandleRewardedAdClosed(object sender, EventArgs args)
     {        
            Debug.Log("HandleRewardedAdClosed");
     }
 
     public void HandleUserEarnedReward(object sender, Reward args)
     {
         string type = args.Type;
         amount = args.Amount;
         ffm.SetDiamonds(ffm.GetDiamonds() + (int)amount);
         Debug.Log("UserEarnedReward");
     }
 
 #endif
 }