@krnel in his post https://steemit.com/cybersecurity/@krnel/setting-up-a-linux-vps-securely-pt-2 advise to remove it and I followed all his advise.

"Remove IPv6 listening
Since no one really uses IPv6 yet, disable this and make one less thing your system is checking for.
AddressFamily inet needs to be added.
You can add this manually to the end of the sshd_config file @ nano /etc/ssh/sshd_config."