Inconsistent Script

[Lumbdi]

I'm generating a geometry using a script in spaceclaim. It used to work in other projects, but since I  swapped from 24R2 to 25R1 it's inconsistent and only works sometimes.
It makes a 2D plane

sectionPlane = Plane.PlaneXY
result = ViewHelper.SetSketchPlane(sectionPlane, None)

and adds lines

result = SketchLine.Create(start, end)

I then want to make named selections, but these lines get sometimes added to FFF/Sketching Plane1 / Sketch1 and sometimes to FFF / Surface (which is how it used to work).
If i delete the sketchContainer1, i get an alternating once it works and then it doesn't behaviour 

selection = SketchContainer1
Delete.Execute(selection)

How do i make this consistent?