didRegisterForRemoteNotificationsWithDeviceToken is not calling after two or three execution

Question

In app , i am trying to implement push notification , supports iOS 7 in xcode 7.3 .

after couple of running , now the didRegisterForRemoteNotificationsWithDeviceToken is not called , this is a very strange issue , the device that im running has iOS 9.3.2

here is my functions in appdelegate

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    // Override point for customization after application launch.

    // self.registerForPushNotificationSystem(application)

//        let settings = UIUserNotificationSettings(forTypes: [.Alert, .Badge, .Sound], categories: nil)
//        UIApplication.sharedApplication().registerUserNotificationSettings(settings)

    let notificationTypes: UIUserNotificationType = [UIUserNotificationType.Alert, UIUserNotificationType.Badge, UIUserNotificationType.Sound]
    let pushNotificationSettings = UIUserNotificationSettings(forTypes: notificationTypes, categories: nil)

    application.registerUserNotificationSettings(pushNotificationSettings)
    application.registerForRemoteNotifications()

    return true
}

func application(application: UIApplication, didRegisterUserNotificationSettings notificationSettings: UIUserNotificationSettings) {
    if notificationSettings.types != .None {
        application.registerForRemoteNotifications()
    }
}

func application(application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: NSData) {
    let tokenChars = UnsafePointer<CChar>(deviceToken.bytes)
    var tokenString = ""

    for i in 0..<deviceToken.length {
        tokenString += String(format: "%02.2hhx", arguments: [tokenChars[i]])
    }

    print("Device Token:", tokenString)
    WebClient.sharedInstace.resgisterNotification(tokenString)
}

what might be the issue this was perfectly working fine yesterday