After running sysprep on cloned virtual machine as explained here:
libvirt work flow explained
The host ssh keys will be wiped from the guest image (this is a good thing) meaning that you will no longer be able to ssh into that guest VM (this is a bad thing).
Fortunately this easy fix.
On Ubuntu, to regenerate new ssh host keys with this simple command
$ sudo dpkg-reconfigure openssh-server
if successful yoou will get something like
Creating SSH2 RSA key; this may take some time ... 2048 SHA256:ToJkgjGdbcFX4wCsiM0IGjGkdSCex3m/ycnsRo0qEA root@UbuntuLTS-clone (RSA) Creating SSH2 DSA key; this may take some time ... 1024 SHA256:Ug9fJa14YMR9Fud/7bXTokffK/hM/sBVse10nSR/6Y8 root@UbuntuLTS-clone (DSA) Creating SSH2 ECDSA key; this may take some time ... 256 SHA256:Rh6izWEXkCV6HZLIpzlGQje178vhDgb77ItaZgpDsIQ root@UbuntuLTS-clone (ECDSA) Creating SSH2 ED25519 key; this may take some time ... 256 SHA256:UD4b7njwxWp1Q3wYf2R//udgPRzfGaeZ/6kE3VgZM+s root@UbuntuLTS-clone ED25519)
Restart your ssh server
$ sudo systemctl restart sshd.service