UIView detaches from bottom of UICollectionView on scroll

I have a UICollectionView that allows a user to enter reps via a UIView containing a picker. The picker container attaches to the bottom of the view as long as the UICollectionView doesn't need to scroll. As more cells are added and the view must scroll, my picker container no longer attaches to the bottom of my view. I have attached a screenshot of my issue and code showing how I have attached my pickerContainer to the bottom of my collectionView.

let pickerContainer = UIView(frame: CGRect(x: 0, y: self.collectionView.frame.height - pickerContainerHeight, width: self.collectionView.frame.width, height: pickerContainerHeight))
<....some other code that i dont think matters....>
collectionView.addSubview(pickerContainer)

from UIView detaches from bottom of UICollectionView on scroll