i don't understand what you really want ,
The issued certificate is generated and saved and won't be regenerated until any certificate configuration change (in activity).
It's a very old bug, to avoid users to change his names and issue a certificate to others
See: https://github.com/bozoh/moodle-mod_simplecertificate/issues/56
The generated certificate, is saved in user's private files, so if course is removed the user still can get the certificate
See: