OAuth2Autenticator Completed without Account [Xamarin Android]

I'm facing an issue, I've created some code to be able to login in my app with facebook. The steps are working as expected:

• The external facebook login web page opens
• The Second activity intercept the redirectUrl after a successfull login

At this point OAuth2Autenticator.Completed(object o, AuthenticatorCompletedEventArgs e) is called but e is not authenticated.

My code in ViewModel:

    async Task FacebookAuth()
    {
        var facebookAppId = "0123...";
        _authenticator = new OAuth2Authenticator(
            clientId: facebookAppId,
            scope: "email",
            authorizeUrl: new Uri("https://www.facebook.com/dialog/oauth/"),
            redirectUrl: new Uri("https://www.myRedirectUrl.com"),
            isUsingNativeUI: true
            );
        _authenticator.Completed += Authenticator_Facebook_Completed;
        _authenticator.Error += _authenticator_Error;
        var presenter = new Xamarin.Auth.Presenters.OAuthLoginPresenter();
        presenter.Login(_authenticator);
    }

In the interceptor activity:

    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        var mUri = new Uri(Intent.Data.ToString());
        _authenticator.OnPageLoading(mUri);
        Finish();
    }

Back to the viewModel:

    private async void Authenticator_Facebook_Completed(object sender, AuthenticatorCompletedEventArgs e)
    {
        _authenticator.Completed -= Authenticator_Facebook_Completed;
        if (e.IsAuthenticated)
        {
            var acc = e.Account;
            var val = JsonConvert.SerializeObject(e.Account);
            var model = JsonConvert.DeserializeObject<FacebookSigninModel>(val);
            var user = await GetFacebookProfile(model.Properties.AccessToken);
            await SignInToAPI(new APIUser
            {
                TokenId = model.Properties.AccessToken,
                Email = user.Email,
                FamilyName = user.FirstName,
                GivenName = user.LastName,
                Picture = user.ProfilePic
            }, AuthProvider.Facebook);
        }
    }

Here e is not authenticated and i have a null account.

Another strange detail is that even if i remove the line:

_authenticator.OnPageLoading(mUri);

the method Authenticator_Facebook_Completed is called anyway with the exact same result.

I've also tried to change the redirect url in order to no catch it in the interceptor activity. So as expected i have to manually go back to my app. Whe the system returns to my app, the Authenticator_Facebook_Completed method is called with parameter values equals to the other approaches.

I have written my code following this sample:

https://github.com/coolc0ders/SocialAuthXamarinFormsAspNetCore/tree/master/AuthDemoXForms

Running this app the Authenticator_Facebook_Completed is called only after the _authenticator.OnPageLoading(Uri); is called too and not when the system reopens the app after the redirect from the web page.

I cannot figure out why my Authenticator_Facebook_Completed is always called no matter what and why _authenticator.OnPageLoading(mUri); has no relevance at all in my code.

Thanks,