Just to give feedback (even if there was a long pause). This preseed issue always happened at 17%. It is not related to network issues.
After (I guess a timeout) the VM reboots and you can login. Then you will notice that /sbin/start-stop-daemon is missing entirely. So a lot stuff is not working. But if you copy this file from another VM to this one and run Puppet, everything works again.
Right now I am doing an upgrade marathon from 2.0 → 3.4 to see if the problem disappears. But troubleshooting and asking here for help with this old version seems not fair.
But it is a long journey since the updates are sequential. Also I run into this one Foreman does not start after OS upgrade due to an OS upgrade. But now 3.0 is running and I can continue.
I guess at some point the guy that was setting up Foreman change it to our needs.
Then we never touched the templates we are using again. Could it be possible that we just have to take the new default one and add our changes into this one? Or: Is it required to update the templates from time to time?