TableView Cells appear and disappear immediately afterwards

I try to insert a viewcontroller with a tableview inside into another viewcontroller. The cells appear and then disappear after 1 second. I have already tried viewWillAppear() to reload the data but it doesn't work.

The first Class is a normal Viewcontroller with a tableview inside

class P1ViewController: UIViewController,UITableViewDataSource,UITableViewDelegate {

var liste:[String] = ["num1", "num2", "num3", "num4"]

@IBOutlet var tabview: UITableView!

override func viewDidLoad() {
     super.viewDidLoad()
 }

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

    return liste.count
}

 func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    return CGFloat(60)
}


 func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell = self.tabview.dequeueReusableCell(withIdentifier: "symptomCell", for:indexPath) as! BulletTableViewCell
    cell.textLabel!.text = self.liste[indexPath.row]
    return cell
}


 }


class BulletTableViewCell: UITableViewCell  {

override func awakeFromNib() {
    super.awakeFromNib()
}
}

The second class is another Viewcontroller. Here i want to push the viewcontroller above.

class TestViewController: UIViewController {


@IBOutlet var contentstack: UIStackView!


override func viewDidLoad() {
    super.viewDidLoad()
    drawBlock()
}

func drawBlock(){

    let iController = self.storyboard?.instantiateViewController(identifier: "p1") as! P 
    P1ViewController   // HERE IS THE ViewController with the tableview inside

    self.contentstack.addArrangedSubview(iController.view)
}

}