Custom Webform handler not working on Wizard Webform
Hopefully this will help someone out there but this is the code I finally got working.  It takes the serial value from a webform submission and writes a Png barcode for use in emails.  I'm using the Barcodes Module for Drupal 8.
use Com\Tecnick\Barcode\Barcode as BarcodeGenerator;

class BarcodeHandler extends WebformHandlerBase {
  /**
   * {@inheritdoc}
   * Write PNG barcode for registration emails
   */
 public function postSave(WebformSubmissionInterface $webform_submission, $update = TRUE) {
   $regId = $webform_submission-&gt;serial();
   $type = 'C39';
   $barcode_file = 'registration/barcodes/' . $regId . '.png';
   $barcode = new BarcodeGenerator();
   $barcode_obj = $barcode-&gt;getBarcodeObj($type, $regId, 250, 50, 'black');

   file_put_contents($barcode_file, $barcode_obj-&gt;getPngData());
      
  }
}