I found similar issue discussed and solved here: [SOLVED] Problem with Client search results
Tried to check it in my environment, but returns error:
Do I really need to re-install with upgrade option?
zimbra@mail:~$ zmprov gs `zmhostname` | grep convertd
zimbra@mail:~$ zmconvertctl status
convertd is not running.
zimbra@mail:~$ zmconvertctl start
Starting convertd...httpd: Could not open configuration file /opt/zimbra/convertd/conf/httpd.conf: No such file or directory