When the RowSpan value is bigger than the available rows, a ArgumentOutOfRangeException is thrown while exporting the document.

Workaround: Change the value of RowSpan after importing:

foreach (var cell in document.EnumerateChildrenOfType<TableCell>())
{
    while (cell.RowSpan > cell.Row.Table.Rows.Count)
    {
        cell.RowSpan--;
    }
}