Thank you all for the testing, importing by level worked for my test data in my set of configuration but the other options like single element or fence are still failing. Defining the blue lines as contures doesn't matter for that issue, the error is still there.
I'll call Bentley InRoads Support again if the issue occurs again.
But does anyone know an option to get the detailed error description in InRoads SS2 like it appeared in former versions? In the past we had the chance to spot the point of the issue since coordinates have been displayed. Now it tells me "No point found". The messages I mean are attached to my initial post.
Thank you all for support!
Maik