jQuery csv file export fires multiple times
Try this:

(function ($) {
  Drupal.behaviors.ons_line_item_export = {
    attach: function (context) {
      $("#edit-export-csv-button").once().click(function() {
        $("#ons-line-item").tableExport({ type: "csv" });
        return false;
      })
    }
  };
})(jQuery);


I added the jQuery.once() method.