Hi Rolf, I had a look at your file and unfortunately Rhino is really bad at splitting meshes. It might be true that this is all due to bad meshes, but it doesn’t change the fact that users need all kinds of meshes split.
The simplest examples I have found is shown here:
And if you take a look at this file part of your file and try to run a meshintersection on the two parts you will see that it messes up. This is typical for how rhino handles mesh intersections when it fails. meshsplit meshintersect bug.3dm (188.5 KB)