Thank you Igor - it seems that the service is not running on startup even there is an entry at /etc/init.d :-(
I even tried to set up a cronjob (@reboot).
Doesn't work :-(
This is what its look like after reboot (connected via serial):
root@bpii:~# /etc/init.d/ssh status
● ssh.service - OpenBSD Secure Shell server
Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
Active: inactive (dead)
root@bpii:~#
Ok, seems that when I'm connected via serial it is in emergency mode - I have to shut it down completely (shutdown -h now) disconnect power and FTDI, and connect power again.
Now it works...