Whenever a new site is added, apache has to be restarted in order to read in the new VirtualHosts with SSL certificates. If only a reload is done with new certificates, apache will complain and say that a full restart is required. So it might just people people adding sites, or it may be some cron as mentioned in the previous post.
You can check if it's DA by having a look at the /var/log/directadmin/system.log
John