Python Crashing In Rhino 5 After I Installed Rhino 6 WIP

Developing an auto NURBS surfacing script here:

http://www.grasshopper3d.com/photo/auto-nurbs-surfacing-of-meshes

...I find that my usually very reliable Python script to use parallel execution to access the Rhinocommon patch command is now crashing like crazy in Rhino 5 after I installed Rhino 6 WIP and thus also had to upgrade IronPython.

In this test file, internalized, there are 733 collections of 3D curves that I'm creating 733 patches from. It works fine on 10 patches at a time, but crashes with much over 300. This works just fine in Rhino 6 WIP with thousands of patches, and it's not a memory issue in the Task Manager at all since memory use doesn't even creep up during execution.

I tried re-saving from Rhino 5 after even recreating the Python script component, in case a newer version was getting pasted into the Rhino 5 Grasshopper canvas, to no avail.

I don't think it's a coding error since it works so well in Rhino 6 WIP.

If Rhino 5 users could confirm it works or not with all the patches selected via the menu I included, I'd feel better sticking to Rhino 6 WIP myself yet still posting scripts that will evidently work for other users.

Does this work in your Rhino 5 set up when you increase the End value to include more and more patches?