Firebase – Why is part of my code not executed if I enable/disable Unity gameObject?

I was using PlayFab and decided to migrate to Firebase.
I want to use FirebaseAuth to implement a login system in my Unity game (and removed the PlayFab code).

So I made a FirebaseManager.cs class, and modified the Script Execution Order to make it run before any other custom script.

I tried to implement what is necessary to create an account and it works great.
I know Firebase silently keeps the user connected between sessions. So I want to check wether a user is already connected or not, from my "home scene" (which is also the scene where you login/create account).

public class FirebaseManager : MonoBehaviour
{
    private static FirebaseManager _instance;
    public static FirebaseManager Instance { ... }

    private FirebaseApp _app;

    private FirebaseAuth _auth;
    public FirebaseAuth Auth
    {
        get
        {
            if (_auth == null)
            {
                _auth = FirebaseAuth.GetAuth(_app);
            }
            return _auth;
        }
    }

    private FirebaseUser _user;
    public FirebaseUser User
    {
        get
        {
            return _user;
        }
        set
        {
            _user = value;
        }
    }

    // Events to subscribe to for this service
    public delegate void FirebaseInitialized();
    public static event FirebaseInitialized OnFirebaseInitialized;
    
    private void Awake()
    {
        if (_instance == null)
        {
            DontDestroyOnLoad(this.gameObject);
            _instance = this;
            InitializeFirebase();
        }
        else { Destroy(this.gameObject); }
    }

    private void InitializeFirebase()
    {
        Debug.Log($"FirebaseManager.cs > INITIALIZING FIREBASE");
        Firebase.FirebaseApp.CheckAndFixDependenciesAsync().ContinueWith(task =>
        {
            var dependencyStatus = task.Result;
            if (dependencyStatus == Firebase.DependencyStatus.Available)
            {
                // Create and hold a reference to your FirebaseApp,
                // where app is a Firebase.FirebaseApp property of your application class.
                _app = FirebaseApp.DefaultInstance;

                // Create and hold a reference to FirebaseAuth
                _auth = FirebaseAuth.DefaultInstance;

                // Create and hold a reference to already logged in user (if any)
                _user = _auth.CurrentUser;

                if (OnFirebaseInitialized != null) OnFirebaseInitialized.Invoke();
            }
            else
            {
                UnityEngine.Debug.LogError(System.String.Format(
                  "Could not resolve all Firebase dependencies: {0}", dependencyStatus));
                // Firebase Unity SDK is not safe to use here.
            }
        });
    }

    private void OnDestroy()
    {
        if (_auth != null) _auth = null;
    }
}

I also made a static AuthService.cs class to call from my scene :

public static class AuthService
{
    private static FirebaseAuth auth = FirebaseManager.Instance.Auth;
    
    public static bool IsUserAlreadyLoggedIn()
    {
        Debug.Log($"AuthService.cs > Checking if user already logged in");
        return auth.CurrentUser != null;
    }
}

Then in my Login Scene, I have this LoginManager.cs class :

public class LoginManager : MonoBehaviour
{
    // Loading Animation
    [Header("Loading Animation")]
    public GameObject loadingAnimation;

    private void Awake()
    {
        FirebaseManager.OnFirebaseInitialized += OnFirebaseInitialized;
    }

    private void Start()
    {
        ShowLoadingAnimation(true);
    }

    private void OnFirebaseInitialized()
    {
        if (AuthService.IsUserAlreadyLoggedIn())
        {
            Debug.Log($"Already LoggedIn");
            OnLoginSuccess();
        }
        else
        {
            Debug.Log($"No User LoggedIn");
            ShowLoadingAnimation(false);
        }
    }

    private void OnLoginSuccess()
    {
        ShowLoadingAnimation(false); // From here, no code is executed
        Debug.Log($"Logged In as: {FirebaseManager.Instance.Auth.CurrentUser.Email}");
        // SceneLoader.Instance.Load(SceneLoader.Scene.CharacterCreation);
    }

    private void OnDestroy()
    {
        FirebaseManager.OnFirebaseInitialized -= OnFirebaseInitialized;
    }

    /// <summary>
    /// Show or Hide the Loading Animation
    /// </summary>
    /// <param name="show">True = show || False = hide</param>
    private void ShowLoadingAnimation(bool show)
    {
        loadingAnimation.SetActive(show);
    }
}

The Loading animation gameObject is just an animated image (+ another image which is used to block user input).

Whenever the code reaches the ShowLoadingAnimation() method. All code after it is NOT executed. But if I remove all the calls to ShowLoadingAnimation(), everything works fine.
The same logic was working fine with PlayFab.

I just don’t understand what is happening. Maybe something to do with threads? Or maybe just my Firebase implementation is wrong? What can I do?

Thanks.