Hey everyone,
just to have this one updated (and probably closed): The issue was identified as a bug in the HGV Graph Storage (`ArrayIndexOutOfBoundsException` during core graph preparation for hgv · Issue #1181 · GIScience/openrouteservice · GitHub) and @andrzej has already found a solution. For me, I have copied his updated code and it works perfectly, so I guess with one of the next commits the problem will be solved for everyone.
Thanks @andrzej for your effort!
Best regards