Scene Transition goes black when i go back to the menu

I made scenes transitions with this video

and it works until i want to come back to the menu, because i go back but the fade in doesn't work and stays black, this is my script if anyone can help please

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.SceneManagement;
5.  
6. public class LevelLoader : MonoBehaviour
7. {
8.     public Animator transition;
9.  
10.     // Update is called once per frame
11.     void Update()
12.     {
13.     }
14.  
15.     private void Start()
16.     {
17.         transition.SetTrigger("End");
18.     }
19.  
20.     private void OnTriggerEnter2D(Collider2D collision)
21.     {
22.         if (collision.gameObject.CompareTag("Foto"))
23.         {
24.             LoadNextLevel();
25.             Destroy(collision.gameObject);
26.         }
27.     }
28.  
29.     public void LoadNextLevel()
30.     {
31.         StartCoroutine(LoadLevel(SceneManager.GetActiveScene().buildIndex + 1));
32.     }
33.  
34.     IEnumerator LoadLevel(int levelIndex)
35.     {
36.         transition.SetTrigger("Start");
37.         yield return new WaitForSeconds(1);
38.         SceneManager.LoadScene(levelIndex);
39.     }
40. }