A 'closed line'?

Good day. Student here at a community college. We have SheetCam on a Plasma in our Prototype Lab. I have been trying to cut out a project but the tool path is wrong. I use Autocad to blow up and join my geometry into polylines. But when I import the drawing it creates a tool path that is not on the drawing. When I go back to Autocad and check properties, it is not a ‘closed line’.

Wondering if i need to go to back to Autocad and ‘close’ all my lines? I have messed with this before and closing those lines changed that geometry in the Autoad drawing. Has anyone come across this before?

You can increase the “Import link tolerance” in application options: