Okay, found it myself - seems as I ran into https://github.com/influxdata/influxdb/issues/21967
Removed Type=forking from /etc/systemd/system/multi-user.target.wants/influxdb.service and finally my database is up again - just lost two hours of data.
(auth-enabled = false in my setup)
Thought quality management of the releases is a bit better 
Now I’m alerted for next time…
