Xamarin.Forms iOS DidReceiveNotificationResponse not called

I am trying to use local notifications in my Xamarin.Forms iOS application.

The notification is visible, but when I tap the notification, DidReceiveNotificationResponse is not called at all. The code that manages the authorization is not shown here but it is correct.

I have read all the posts here and elsewhere about this problem that seams to be related to a delegate issue (not assigned).

Here is my code:

[Register("AppDelegate")]
public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate, IUNUserNotificationCenterDelegate
{
    public override bool FinishedLaunching(UIApplication app, NSDictionary options)
    {
        Popup.Init();
        global::Xamarin.Forms.Forms.Init();

        UNUserNotificationCenter.Current.Delegate = this;

        ...
    }

    [Export("userNotificationCenter:didReceiveNotificationResponse:withCompletionHandler:")]
    public void DidReceiveNotificationResponse(UNUserNotificationCenter center, UNNotificationResponse response, System.Action completionHandler)
    {
        if (response.IsDefaultAction)
        {
            if (response.Notification.Request.Content.UserInfo.ContainsKey(new NSString("remainingTime")))
            {
                Locator.GetSharedInstance<IAlertDelayedService>().RaiseOpenAlertDelayedPopupEvent();
            }

        }
        completionHandler();
    }

    [Export("userNotificationCenter:willPresentNotification:withCompletionHandler:")]
    public void WillPresentNotification(UNUserNotificationCenter center, UNNotification notification, System.Action<UNNotificationPresentationOptions> completionHandler)
    {
        completionHandler(UNNotificationPresentationOptions.Alert);
    }

}

I have found a solution in a Xamarin.Forms notification sample here.
It uses a UNUserNotificationCenterDelegate derived class to handle the received and tapped notifications.