Imported PDF lines incomplete

A path cannot exist without at least 2 anchor points, so I'll assume you didn't understand the question.

I'm not a CAD operator, so my knowledge of it is limited, but I work with a lot of CAD-origin stuff. I see this from time to time, especially in cases where 'perspective' or perhaps other 2D CAD-based render-to-screen techniques have been applied. I suspect that cylindrical effect is borne of such a technique. The underlying, original CAD vectors are "stretched," figuratively speaking. They maintain the effect (and their perceivable integrity) in the native format, but it outside of the CAD environment, they break up as you see. It's possible there are unstroked anchors in those gaps. If you Select All (in Illustrator), you will see them, if they're there.

Otherwise, if you have access to the orginal, native file or the person who built it, there may be other ways to get around it.