You operator is being overly fussy or is using some antiquated processes that require a continuous string. Routers for instance tend to stop/start and endpoints, but it is their software that needs to solve continuity. Even polyline files are individual line segments.
I just went through a similar issue with an AI operator that couldn't take DXF or DWG (huge spline files). Neither polylines not splines worked. I ended up sending plot files (EPS) which are generated as *.plt, but a rename to *.eps will make AI recognized the file. I could open the file in Photoshop Elements and select the resulting string for a mask edge and fill the interior. If that's not enough for your operator, they need some classes.
The problem stems from the recognition of most vector exports or primitives. Lines, arcs, circles ellipses, polylines (if not splines) which is how these expoprt files are written for over a decade. I get so much flack from CNC operators and illustrators that I add 2 days for conversion issues alone. The problem is not on PTC's end, it is the huge influx of poorly trained operators and really poor implementations in their "tool of choice". The biggest problem is data integrity. Once the operator finishes massaging the file, I want an output from their system to confirm the data is still within my design intent.