One list of closed polyline curves moved in z direction and tried to loft together, shows error ! 1. Solution exception:Index was out of range. Must be non-negative and less than the size of the collection.
The issue is you have a null curve in the bottom move list.
Which I tracked down to being this triangle.
and that is because the way you are making planes, you use points at index 0,1, and 3. But a triangle doesn’t have a point at index 3 so you get a null plane there.
Solution: Change the 3 to a 2 so it works with potential triangles and all works fine.
Thank you so much, you are an amazing mentor !