title: Camera freezes when I come back to viewcontroller containing ARSCNView. How to come and go in this view controller without ARSCNView stop working?
body: <p>How I initialize the ARSCNView</p>
  
  <pre><code>var sceneView: ARSCNView?
  
  override func viewDidLoad() {
      super.viewDidLoad()
      if ARConfiguration.isSupported{
          sceneView = ARSCNView(frame: CGRect(x: 0, y: 0, width: UIScreen.main.bounds.size.width, height: UIScreen.main.bounds.size.height))
  
          view.addSubview(sceneView!)
  
          sceneView!.delegate = self
          // Show statistics such as fps and timing information
          sceneView!.showsStatistics = false
  
          // Create a new scene
          let scene = SCNScene(named: "totens.scnassets/Main.scn")!
          // Set the scene to the view
          sceneView!.scene = scene
       }
    }
  
  override func viewWillAppear(_ animated: Bool) {
      super.viewWillAppear(animated)
  
          guard let referenceImages = ARReferenceImage.referenceImages(inGroupNamed: "TotensImages", bundle: nil) else { return }
  
          let configuration = ARImageTrackingConfiguration()
          configuration.trackingImages = referenceImages
          let options: ARSession.RunOptions = [.removeExistingAnchors]
  
          sceneView!.session.run(configuration, options: options)
   }
  </code></pre>
  
  <p>When a dismiss this view controller and try to restart session the camera stop appearing.
  Someone knows how to help me with this? thanks</p>