The WebGL version of my game does not load the next scene when using an async action

I've just created a WebGL build for my puzzle game in Unity. While the Windows version worked just fine, I encountered a bug on the web: it cannot load the next level when you collide with the goal.

Here is the code:

//PlayerInteraction.cs
private void OnTriggerEnter2D(Collider2D collision)
{
    if (collision.TryGetComponent(out ReactToPlayer component))
    {
        component.React(gameObject);
    }
}

public class GoalReactToPlayer : ReactToPlayer
{
    public override void React(GameObject player)
    {
        EventBus<WinEvent>.Raise(new WinEvent());
    }
}

public class GameController: MonoBehavior
{
  private void OnEnable()
  {
    
    _winEventBiding = new(WinAction);
    EventBus<WinEvent>.Register(_winEventBiding);
  }
 private async void WinAction(WinEvent @event)
 {
    await Task.Delay(500);
    var a = _sceneTransitioner.LoadNextScene();
    a.completed += a => Reload();
 }

public class SceneTransitioner : MonoBehaviour
{
    public AsyncOperation LoadNextScene()
    {
        DOTween.KillAll();
        int index = SceneManager.GetActiveScene().buildIndex;
        var a = SceneManager.LoadSceneAsync(index + 1,LoadSceneMode.Single);
        return a;
    }
}

Here is the game on itch.io.

How can I debug this?