As you said, it looks like an issue on the atv1 box.
I have no practical experience of using an atv1, but if SSH is borked, you’ll either need to get keyboard CLI access or I guess it’s reinstall time.
If you do get CLI access, I’d first check if SSH is enabled and running: systemctl status ssh.
You can also recreate the SSH keys with sudo dpkg-reconfigure openssh-server. (You might need to delete the old ones first - /etc/ssh/ssh_host_*)
Finally, you can always reinstall SSH server: sudo apt-get install --reinstall openssh-server