UICollectionView drop delegate not called with multiple items

I'm working on implementing drag and drop to rearrange items in my UICollectionView. The issue I'm running into is that my drop delegate's collectionView(_, performDropWith:) method isn't getting called when the drag has multiple items. With single item drags, it works fine. What would cause it to break with multiple items?

I've replicated it in a basic sample app. Below is the drop delegate.

class CollectionDropDelegate: NSObject, UICollectionViewDropDelegate {
    let controller: MainViewController

    init(controller: MainViewController) {
        self.controller = controller
    }

    func collectionView(_ collectionView: UICollectionView, canHandle session: any UIDropSession) -> Bool {
        session.localDragSession != nil
    }

    func collectionView(_ collectionView: UICollectionView,
                        dropSessionDidUpdate session: any UIDropSession,
                        withDestinationIndexPath destinationIndexPath: IndexPath?) -> UICollectionViewDropProposal {
        if session.localDragSession != nil {
            .init(operation: .move, intent: .insertAtDestinationIndexPath)
        }
        else {
            .init(operation: .cancel)
        }
    }

    func collectionView(_ collectionView: UICollectionView,
                        performDropWith coordinator: any UICollectionViewDropCoordinator) {
        let destinationPath = coordinator.destinationIndexPath ?? IndexPath(item: 0, section: controller.items.count)

        for item in coordinator.items {
            guard let draggedItem = item.dragItem.localObject as? NumberItem,
                  let currentIndex = controller.items.firstIndex(of: draggedItem)
            else { continue }
            controller.items.remove(at: currentIndex)
            controller.items.insert(draggedItem, at: destinationPath.item)
            coordinator.drop(item.dragItem, toItemAt: destinationPath)
            collectionView.moveItem(at: IndexPath(item: currentIndex, section: 0),
                                    to: destinationPath)
        }
    }
}