We recently added a mirror server as a backup to our existing ispconfig web and mail server (ubuntu 16.04 nginx php-fpm ispconfig3 - hosting mutliple websites and cms). We shared the necessary folders (the master machine running a NFS server sharing /var/www and the /etc/letsencrypt/ and /usr/local/ispconfig/interface/acme). Soon after activating the mirror we noticed missing LE checkboxes for all the sites in ispc. After activating the option "Let's Encrypt SSL" for a site again the letsencrypt.log shows a successful renewal attempt, but soon after we receive a mail with "WARNING - Let's Encrypt SSL Cert for: domain.tld could not be issued.". Those mails seem to always be sent from the mirror server. The certs are ok and keep working fortunately but the checkbox gets unchecked and we have to take care not to save a site with the box uncheck to avoid loosing TLS. It is the same when creating a new cert the log shows no problems, we get the new working cert and all looks fine besides the fact that after a minute the checkbox is unchecked. Please advise how to deal with this situation. All we need from this mirror server is to act as a backup slave - we have deactivated the ../server/lib/classes/conf.d/500-backup skript on the master by renaming. Maybe this has an effect? We do not understand why there is a feedback coming from the mirror that most likely causes the option to get unchecked at the panel. The master was running fine for quite a while until the mirror was added and nothing else was changed. We ridded letsencrypt from entries that caused errors to show up within the logs of both servers, to be sure that there is no general reaction because of a failing exit code from letsencrypt or something like that. We have ntp time synchronization via ubuntu ntp server package on both servers. Version on both servers identically letsencrypt 0.4.1 Last but not least, thanks a lot for maintaining this great product and for beeing active in the forum!