that's the check by the certificat-module:
} else if ($cm->module == $feedid) {
return (get_record('feedback_completed', 'id', $cm->instance, 'userid', $userid) !== false);
It looks good as far as I can see.
There may be an other problem. But I can't find it
I did not work often with the certificate-module. Try to ask the developer of this module.
Andreas