Splitting Cylinders - not easy?

I am struggling to split a cylindrical extrusion uncapped with a vertical plane in Grasshopper. I wasn’t able to get the operation to work with baked geometry. Here is a screenshot showing the issue:

Basically, with the baked geometry the cylinder splits at the intended plane and at the edge/seam of the extrusion, even though I only specified one surface to split.

When I perform the identical operation in GH, it shows a warning that the split did not succeed.

In my previous design iteration I was splitting both cylinders across the XZ plane, right on the seam, so I guess I didn’t encounter any of these issues. But basically my question is how do I split the cylinder with a vertical plane in Grasshopper?

Here’s the internalized data
split-fail.gh (3.9 KB)
and a clearer screenshot


I ended up creating arcs and extruding them