In 1.2.4 when we deploy OVA without defined hostname, - default hostname is debian, propose change it to vyos.
https://github.com/vyos/vyos-cloud-init/blob/current/cloudinit/config/cc_vyos.py#L145 replace to
if hostname != '':
config.set(['system', 'host-name'], value=hostname, replace=True)
else:
config.set(['system', 'host-name'], value='vyos', replace=True)