Please login as the user "ubuntu" rather than the user "root" FIX

sudo nano /root/.ssh/authorized_keys

Удалить всё до rsa ключа (нижеприведённую часть):

no-port-forwarding,no-agent-forwarding,no-X11-forwarding,command="echo 'Please login as the user \"ubuntu\" rather than the user \"root\".';echo;sleep 10"