title: UICollectionViewFlowLayout estimatedItemSize does not work properly with iOS12 though it works fine with iOS 11.*
body: <p>For UICollectionView's dynamic height cells we use,</p>
  
  <pre><code>if let layout = self.collectionViewLayout as? UICollectionViewFlowLayout {
      layout.estimatedItemSize = UICollectionViewFlowLayoutAutomaticSize
  }
  </code></pre>
  
  <p>with the proper constraint of height and width, it works fine with iOS 11.* versions but it breaks and does not make the cells dynamic for iOS 12.0 </p>