title: UIView.animate with repeat option stops when new View Controller is presented
body: <p>I have a View Controller with one animation that is set to loop indefinitely with <code>options: [.autoreverse, .repeat]</code> - This works perfect, however, when I present a new View Controller (the Settings VC) - then dismiss it to return to the view with the animation, the animation is not animating. The view (<code>ballContainer</code>) just remains static, when it SHOULD still be animating.</p>
  
  <p><strong>animateBallViewIn method</strong></p>
  
  <pre><code>func animateBallViewIn() {
      self.view.layoutIfNeeded()
  
      UIView.animate(withDuration: 0.5, animations: {
          self.ballContainer.alpha = 1.0
      }) { (true) in
  
          UIView.animate(withDuration: 0.5, delay: 0.0, options: [.autoreverse, .repeat], animations: {
              ballViewBottomConstraint = 20.0
  
              self.view.layoutIfNeeded()
          }, completion: nil)
      }
  
  }
  </code></pre>
  
  <p>Note - I'm calling <code>animateBallViewIn()</code> in a property observer.</p>
  
  <p><strong>How can I keep the above animation animating after returning to it from presenting another View Controller?</strong></p>