I still do not understand what you’re trying to achieve with this definition.
The mesh has self intersections which cause problems later on when you are trying to loft the section curves.
You can however tri remesh your bad mesh and turn it into a better mesh.
Lofting curves with such different control point structure is generally a bad idea without rebuilding.
The C# script to calculate the volume is obsolete but I left it.
General advice hower your mouse on inputs / outputs and you would for example see some information on path structure or if a Brep is closed or open…
Invalid curve.gh (64.9 KB)