Spreadsheet example hangs when select and drag header along with cell data

// code placeholder
onPositionChanged: {
                            const position = Qt.point(dragArea.mouseX, dragArea.mouseY)
                            // cell is the cell that currently mouse is over it
                            const cell = tableView.cellAtPosition(position, true)
                            // dropCell is the cell that it was under the mouse's last position
                            // if the last and current cells are the same, then there is no need
                            // to update highlight, as nothing is changed since last time.
                            if (cell === dropCell)
                                return
                            // if something is changed, it means that if the current cell is changed,
                            // then clear highlighted cells and update the dropCell.
                            tableView.model.clearHighlight()
                            dropCell = cell
                            // if the current cell was invalid (mouse is out side of the TableView)
                            // then no need to update highlight
                            if (cell.x < 0 || cell.y < 0)
                                return
                            // if dragged cell is the same as the (possibly) dropCell
                            // then no need to highlight any cells
                            if (dragArea.dragCell === dropCell)
                                return
                            // if the dropCell is not the same as the dragging cell and also
                            // is not the same as the cell at the mouse's last position
                            // then highlights the target cells
                            for (let i in _spreadSelectionModel.selectedIndexes) {
                                const old_index = _spreadSelectionModel.selectedIndexes[i]
                                let cell = tableView.cellAtIndex(old_index)
                                cell.x += dropCell.x - dragArea.dragCell.x
                                cell.y += dropCell.y - dragArea.dragCell.y
                                const new_index = tableView.index(cell.y, cell.x)
                                tableView.model.setHighlight(new_index, true)
                            }
                        }