Ok to duplicate the problem start with a blank conf file or with one line of "#" only on first line. Then edit the conf with webmin for example: edit the potocal then save once, then do a second edit, and add the cert files with diretory and cert info, this ads the incorrect old conf tags (ssl_cert_file , ssl_key_file ). In webmin 1.955.
Dovecot and Webmin Conflict with Config