Remote access using ssh - not windows

I am trying to remotely shutdown a music server (Vortexbox) using the command_line component. I have used this page (http://linuxproblem.org/art_9.html) to access the server from HassIO without needing a password.

It all works fine until I reboot HassIO, then I get a message “The authenticity of host ‘xxx.xxx.x.x (xxx.xxx.x.x)’ can’t be established”.

What I have found is that the .ssh directory and files (id_rsa and id_rsa.pub) that were created to access the remote server without password have disappeared during the HassIO reboot. Is this behaviour a consequence of using HassIO or should I follow a different procedure?

Not sure whether related, but I also need to manually start the SSH addon at reboot even though it is meant to ‘Start on boot’.