SSH uses ephemeral diffie hellman which gives you forward secrecy, meaning that recorded sessions can't be decrypted later if the server private key is compromi

SSH uses ephemeral diffie hellman which gives you forward secrecy, meaning that recorded sessions can't be decrypted later if the server private key is compromised. So sessions sniffed in the past can't be decrypted using the private key that was shared among VM's. So provided that all server owners immediately change their keys and no one was man-in-the-middled before Hetzner announced this, everyone should stay secure. I very much doubt anyone was MITM'd because it would be difficult and the prize for MITM'ing a Hetzner server isn't that motivating.