I can login to a root shell on my machine (yes or no, or I don't know): yes
I have received next warning:
Your certificate (or certificates) for the names listed below will expire in 19 days (on 20 Nov 16 11:18 +0000). Please make sure to renew your certificate before then, or visitors to your website will encounter errors. git.kanteron.com
But as I can see with my browser and with this webpage certificate is properly renewed and will expire in 82 days (rather than 19).
Certificate was renewed 1 week ago and I have received the warning today.
Let’s Encrypt only treats a certificate as a “renewal” if the DNS names are exactly the same. The certificate the notification is about was issued just for the name “git.kanteron.com” but you now have a certificate which contains the extra name “forum.kanteron.com” and so although you probably think of this newer certificate as “renewing” from Let’s Encrypt’s point of view it’s a completely different certificate and the old one is still going to expire.
You can safely ignore this notice since you are content to just use the new certificate with both names.
By the way, thankyou for telling us the correct DNS name on the certificate, this makes investigating the circumstances of the situation much easier, for your reference I looked at https://crt.sh/?q=git.kanteron.com the crt.sh service (operated by Comodo, another CA, thanks to them) is a Certificate Transparency log monitor, so it shows all certificates published to the logs. Most but not all certificates are currently logged, including all those signed by Let’s Encrypt.