webform_group module access check assumes that source node param is always present in the current request

I have a similar problem in 2.x version too; i'm trying to give access to a specific group role to all submissions of a specific webform.
In Drupal\webform_group\WebformGroupManager the function getCurrentGroupRelationship return always FALSE due to:
$source_entity = $this->requestHandler->getCurrentSourceEntity(['webform_submission']);
returning always a NULL value fot paths like "node/X/webform/results/submissions".
I tried to extract node parameter from current route but without luck (i found no route name nor route parameters in request using \Drupal::routeMatch()).
As a temporary quick & dirty fix (for nodes only) i use:

    $source_entity = $this->requestHandler->getCurrentSourceEntity(['webform_submission']);
    if (!$source_entity) {
      if (preg_match("/^(\/.*)?\/node\/([1-9][0-9]*)\/webform\/results\/(submissions|download)$/", \Drupal::service('path.current')->getPath(), $matches)) {
        $source_entity = $this->getEntityStorage('node')->load($matches[2]);
      }
      if (!$source_entity) {
        return $this->currentGroupRelationship;
      }
    }

I'm sure that there is a better solution than raw url pattern matching .. any idea is welcome!