I rendered two 4K versions of the scene and this happened....
The black lines are already in the HD version I posted but not too apparent.
They mark the plane of the Depth of Field preview, where the image is in focus.
No idea, why and how to get rid of them. AA was at 6 and 8 and Micropoly Detail at 0.6 and 0.8.
While the HD version renderered ok, in the 4K version the top of the "pilar" is cut of.
I changed some camera setting, the settings for render buckets, the position of the camera very slightly.
Rendering 4K the top always got cut off. Baah

CHeers, Klaus