Hi,
when i convert polyline to CAD using arcpro, it appears as buffer when i open it in autocad software. see the image.
shows fine in arcgis or qgis but not in autocad.
I wonder if you use the Explode tool in the Modify Features pane to make single parts from the polyline, then run the Export to CAD GP tool on the exploded polyline feature class, does the DXF file in AutoCAD now show lines vs polygons?