Swift UIBarButtonItem is hidden but works - ios

Question

I have an problem with an UIBarButtonItem. If I protect my app with an ViewController, to authenticate the User through Touch ID, then the UIBarButtonItem in the Navigation Controller is hidden.
The code in the AppDelegate:
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
let touchIDonoff = UserDefaults.standard.object(forKey: "touchIDActive") as! Bool!
if touchIDonoff == true {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let loginVC = storyboard.instantiateViewController(withIdentifier: "TouchIDViewController") as! TouchIDViewController
self.window?.rootViewController = loginVC
}
return true
}
Code in the ViewController for TouchID-Request:
override func viewDidLoad() {
super.viewDidLoad()
DispatchQueue.main.async {
self.touchIDrequest()
}
#IBAction func buttonTouchID(_ sender: AnyObject) {
touchIDabfrage()
}
func touchIDrequest() {
let authenticationContext = LAContext()
var error: NSError?
if authenticationContext.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {
authenticationContext.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: "Please authenticate", reply: { (success: Bool, error: Error?) in
if success {
self.navigatetoAuthenticatedVC()
} else {
if let evaluateError = error as? NSError {
print(error)
/*let message = self.errorMessageForLAErrorCode(errorCode: evaluateError.code)
self.showAlertViewAfterEvaluatingPolicyWithMessage(message: message)
*/
}
}
})
} else {
showAlertViewForNoBiometrics()
return
}
}
func navigatetoAuthenticatedVC() {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let tabBarController = storyboard.instantiateViewController(withIdentifier: "LoggedInVC") as! UITabBarController
let appDelegate = UIApplication.shared.delegate as! AppDelegate
DispatchQueue.main.async {
appDelegate.window?.rootViewController = tabBarController
}
}
If I hit the hidden UIBarButtonItem it works and bring me to the next ViewController and when I go back, the UIBarButtonItem is visible.
What did I wrong? Any help please?
Best regards