Screen goes black after segue

I have solved the problem! the problem was the order in which the functions were being called.

I realised not that the page was being set up too fast for firebase so I now call the function earlier! in the view will appear

override func viewWillAppear(_ animated: Bool) {
        print("Done")
        super.viewWillAppear(animated)

        self.loadDataFromFirebase()
}

Thanks to all who helped!