8.7.11 zimbra.log and zimbra-stats.log empty

[Luigius]

Hi,
Since updating to 8.7.11 I get zimbra.log and zimbra-stats.log (in /var/log) empty.
rsyslogd is running and in fact maillog contains the log.
If I restart rsyslogd, zimbra.log will start to get data, but not for long.
Rsyslog is running (service rsyslogd status).
rsyslogd.conf is the default one.
OS is Centos 6.9

Any suggestion?

Thanks
Luigi