SceneManager.LoadSceneAsync() problem on Andorid

Hi everyone,

I have use thiss code to load a new Scene and display the progress to the users

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 using UnityEngine.SceneManagement;
 
 public class LoadingScreenManager : MonoBehaviour
 {
 
     [Header("Loading Visuals")]
     public Text loadingText;
     public Image progressBar;
 
     [Header("Loading Settings")]
     public LoadSceneMode loadSceneMode = LoadSceneMode.Single;
     public ThreadPriority loadThreadPriority;
 
     AsyncOperation operation;
     Scene currentScene;
 
     public static int sceneToLoad = -1;
     static int loadingSceneIndex = 1;  // !!!change this 
 
     public static void LoadScene(int levelNum)
     {
         Application.backgroundLoadingPriority = ThreadPriority.High;
         sceneToLoad = levelNum;
         SceneManager.LoadScene(loadingSceneIndex);
     }
 
     void Start()
     {
         if (sceneToLoad < 0)
             return;
         currentScene = SceneManager.GetActiveScene();
         StartCoroutine(LoadAsync(sceneToLoad));
     }
 
     private float currentProgress = 0f;
     private IEnumerator LoadAsync(int levelNum)
     {
 
         yield return null;
         StartOperation(levelNum);
 
         float lastProgress = 0f;
 
         // operation does not auto-activate scene, so it's stuck at 0.9
         while (DoneLoading() == false)
         {
             yield return null;
 
             if (Mathf.Approximately(operation.progress, lastProgress) == false)
             {
                 currentProgress = operation.progress;
                 if (currentProgress < 0.85)
                 {
                     progressBar.fillAmount = currentProgress;
                     loadingText.text = ((int)((progressBar.fillAmount) * 100)) + " %";
                 }
                 else
                 {
                     progressBar.fillAmount = 1;
                     loadingText.text = "100 %";
                 }
 
                 lastProgress = operation.progress;
             }
         }
 
         if (loadSceneMode == LoadSceneMode.Additive)
             SceneManager.UnloadScene(currentScene.name);
         else
             operation.allowSceneActivation = true;
     }
 
     private void StartOperation(int levelNum)
     {
         Application.backgroundLoadingPriority = loadThreadPriority;
         operation = SceneManager.LoadSceneAsync(levelNum, loadSceneMode);
 
 
         if (loadSceneMode == LoadSceneMode.Single)
             operation.allowSceneActivation = false;
     }
 
     private bool DoneLoading()
     {
         return (loadSceneMode == LoadSceneMode.Additive && operation.isDone) || (loadSceneMode == LoadSceneMode.Single && operation.progress >= 0.9f);
     }
 }

Yes, I can load new scene but there is a problem with progress bar when I build for Android devices First, the progress will load to 14%, then return to 0% then load to 100% and switch to new Scene

What's wrong with these code? Why does it return to 0%?

Thanks in advance!