I finally got it working ;D ;D ;D
As I have read in another posting, someone succeeded in deactivating all rules, started suricata, then activated the rules and restarted suricata again. Up from that point, suricata started showing alerts at least.
Afterwards I let suricata rebuild the "Interface SID Management File Assignments", that´s when suricata started blocking packages and showing them red in the alerts view.
So maybe there had been some incompatible rules or settings in the older pfs-version-data I imported in 2.3.
Everything seems to be fine now.
Thanks for your help.