Paths with a stroke color and no fill are still filling random corners within the shape. I've rebuilt the shape, and checked for redundant nodes, but neither has fixed the problem. To make is worse, this is happening to to connection points at random (sometimes it has a fill, sometimes it doesn't). Definitely a bug, and a very major one.

Also, copying the artwork into a new document, or even into InDesign, does not fix it. Placing the artwork in InDesign actually makes the preview glitch out. It's as if Adobe gave CC 2018 a lobotomy!

Screenshot 1: paths in illustrator (randomly filling join points).
Screenshot 2: placing the artwork (as a linked file) in InDesign makes a glitchy preview.