found it out myself!
If you install a license and do write mem + power cycle (meaning power off), the licenses are lost and you have to re-enter them.
If you are doing a reload of the box instead you can see "Syncing database....." on the CLI.
This obviously saves the licenses for next reboot. After that you are also save to power cycle
Tested with 8.3.0.0 and 8.4.0.2