sorry if it took a little to study this definition. I need to start saying that there is no bug.
The operation as laid out with the SrfSplit component is not parallelizable by code. If you run it in parallel, you will get the intersection of each curve, independently. This makes sense – the operation of splitting gives two results (in this case) each time, and you want to use these results in the next splitting operation. This operation is not logically re-dividable in parallel, as you need all results each time.
Instead, you get the split of a copy of the surface with a curve each time. I use ghpythonlib.treehelpes.list_to_tree to visualize the result in Grasshopper.
As usual, parallelism in code is not for a casual look. It need a lot of patience and understanding of the process. However, this new parallelization makes sense if, later, you are able to distinguish the two surface groups (the first one has 3 because there is a seam).
I hope this helps,
for Robert McNeel & Associates
parallel2.gh (270.5 KB)