Splitting Splines

I’m having trouble splitting a spline by another line. In some cases my dynamo script works, in others it produces this error:

Warning: DetailCurve.ByCurve operation failed.
The multiplicities of other interior knots must be at most degree - 2.
Parameter name: knots

Can anyone help me understand what that error message means and how to fix it?

Dynamo graph: split spline.dyn (17.0 KB)
Revit file: tests.rfa (308 KB)

Dynamo Core version:
Dynamo Revit version:
Revit version: 2019.2

The errors appear to happen because of a mal-formed spline (exploded cad most likely.) The solution is to recreate the spline and then perform the operations.