sorry for that - I didn’t add the correct pictures. I’ve edited my post.
My problem was that the i will never see the Landscape actors in selection mode. So
I think i understand why now. I created a copy of SimpleForest provided in the example for PCG. That level seems to have some settinigs preventing Landscape actors to show
When i use another level (eg Third Person default level), and recreate my landscape spline, i can see it.
This might be due to World Partition disabled on the SimpleForest example: i was not able to activate it nor check if it’s active…
The cool thing is that my code which was not working on the Simple Forest level works now 
Thanks for the hint about level partition !