I narrowed down the root cause and its happening when you pin the NSCollectionLayoutBoundarySupplementaryItem that are applied to the layout through UICollectionViewCompositionalLayoutConfiguration .. Here's the narrowed down code that's causing this crash.. func layout() -> UICollectionViewLayout {     UICollectionViewCompositionalLayout(sectionProvider: { [self] section, _ in       // Building section here     }, configuration: configuration)   }         var configuration: UICollectionViewCompositionalLayoutConfiguration {     let configuration = UICollectionViewCompositionalLayoutConfiguration()     var boundaryItems: [NSCollectionLayoutBoundarySupplementaryItem] = [] var offset = 0 for column in 0..<datasource.numberOfColumns {       let columnHeaderSize = NSCollectionLayoutSize(widthDimension: .absolute(100), heightDimension: .absolute(44))       let headerView = NSCollectionLayoutBoundarySupplementaryItem(         layoutSize: columnHeaderSize,         elementKind: "columnHeader",         alignment: .topLeading,         absoluteOffset: CGPoint(x: offset, y: 0)       )       headerView.pinToVisibleBounds = true       headerView.zIndex = 2               offset += 100.0       boundaryItems.append(headerView)     }     configuration.boundarySupplementaryItems = boundaryItems     return configuration   }

Here's the code: func layout() -> UICollectionViewLayout {     UICollectionViewCompositionalLayout(sectionProvider: { [self] row, _ in       var cellItems: [NSCollectionLayoutItem] = []       let rowHeight = NSCollectionLayoutDimension.absolute(44)       var rowWidth: CGFloat = 0.0               for column in 0..<10 {         let cellWidth = NSCollectionLayoutDimension.absolute(100)         let cellSize = NSCollectionLayoutSize(widthDimension: cellWidth, heightDimension: rowHeight)         let cell = NSCollectionLayoutItem(layoutSize: cellSize)         cellItems.append(cell)         rowWidth += width       }       var rowBoundaryItems: [NSCollectionLayoutBoundarySupplementaryItem] = []       var groupOffset: CGFloat = 0.0       if let rowHeader = header(for: row) {         groupOffset = 60         rowBoundaryItems.append(rowHeader)       }       rowWidth += groupOffset               let rowSize = NSCollectionLayoutSize(widthDimension: .absolute(rowWidth), heightDimension: rowHeight)       let group = NSCollectionLayoutGroup.horizontal(layoutSize: rowSize, subitems: cellItems)       group.contentInsets = NSDirectionalEdgeInsets(top: 0, leading: groupOffset, bottom: 0, trailing: 0)        let section = NSCollectionLayoutSection(group: group)       section.boundarySupplementaryItems = rowBoundaryItems       return section     }, configuration: configuration)   }         var configuration: UICollectionViewCompositionalLayoutConfiguration {     let configuration = UICollectionViewCompositionalLayoutConfiguration()     var boundaryItems: [NSCollectionLayoutBoundarySupplementaryItem] = []     if let topLeftItem = topLeftView {       boundaryItems.append(topLeftItem)     }           boundaryItems += columnHeaderItems     configuration.boundarySupplementaryItems = boundaryItems     return configuration   }       var topLeftView: NSCollectionLayoutBoundarySupplementaryItem? {      let columnHeaderHeight = NSCollectionLayoutDimension.absolute(44)     let topLeftCellSize = NSCollectionLayoutSize(widthDimension: NSCollectionLayoutDimension.absolute(60, heightDimension: columnHeaderHeight)     let topLeftCell = NSCollectionLayoutBoundarySupplementaryItem(       layoutSize: topLeftCellSize,       elementKind: "topLeftHeader",       alignment: .topLeading     )           topLeftCell.pinToVisibleBounds = true     topLeftCell.zIndex = 3           return topLeftCell   }       var columnHeaderItems: [NSCollectionLayoutBoundarySupplementaryItem] {     var headerItems: [NSCollectionLayoutBoundarySupplementaryItem] = []     var offset = 60           for column in 0..<datasource.numberOfColumns {       let width = dimensionsProvider.widthForColumn(column)       let columnHeaderSize = NSCollectionLayoutSize(widthDimension: .absolute(100), heightDimension: .absolute(44))       let headerView = NSCollectionLayoutBoundarySupplementaryItem(         layoutSize: columnHeaderSize,         elementKind: "columnHeader",         alignment: .topLeading,         absoluteOffset: CGPoint(x: offset, y: 0)       )       headerView.pinToVisibleBounds = true       headerView.zIndex = 2               offset += width       headerItems.append(headerView)     }           return headerItems   }   func header(for row: Int) -> NSCollectionLayoutBoundarySupplementaryItem? {     let rowHeight = 44     let headerSize = NSCollectionLayoutSize(widthDimension: .absolute(60, heightDimension: .absolute(rowHeight))     let header = NSCollectionLayoutBoundarySupplementaryItem(layoutSize: headerSize, elementKind: "rowHeader", alignment: .leading)     header.pinToVisibleBounds = true     header.zIndex = 1           return header   }

Code is mentioned below