Why does UICollectionView log an error when the cells are fullscreen?

Question

I have a UICollectionViewController using a UICollectionViewFlowLayout where my itemSize is the size of the UICollectionView

Answer 1

I was getting the same error when I was trying to embed a UICollectionView in a UITableView. I was generating a new UICollectionView in each UITableView cell, but I did not put any constraints on the height of that UICollectionView. So, when I put a constraint on the height, that error is gone!