Maybe it's too late with the answer, but I found a solution. I had the same problem myself. It seems that the code is identical, but small details can lead to an error lazy var collectionView: UICollectionView = {         let collectionView = UICollectionView(frame: .zero, collectionViewLayout: CollectionViewLayout().createCompositionaLayout())         collectionView.frame = CGRect(x: 0, y: 0, width: self.bounds.width, height: self.bounds.height)         collectionView.register(PreviewCardPersonCollectionViewCell.self, forCellWithReuseIdentifier: "PreviewCardPersonCollectionViewCell")         collectionView.translatesAutoresizingMaskIntoConstraints = false         collectionView.dataSource = self         collectionView.delegate = self         collectionView.backgroundColor = .red         return collectionView     }() self.addSubview(collectionView)         collectionView(equalTo: self.leadingAnchor, constant: 20).isActive = true         collectionView.trailingAnchor.constraint(equalTo: self.trailingAnchor, constant: -20).isActive = true         collectionView.topAnchor.constraint(equalTo: self.topAnchor, constant: 20).isActive = true         collectionView.heightAnchor.constraint(equalToConstant: 100).isActive = true