I’m trying to make a nice, clean black-and-white drawing. Most of the lines show up just fine. However, a few of the components have curved surfaces that don’t show up. I’ve tried editing styles to make it more visible, but nothing is working.
Checking the profile box allows the pipe to be visible, but not the swivel fitting above it.
The edges in the curved surfaces in your components are hidden, not softened. This seems to make a difference to SketchUp’s ability to generate profile lines. Open the components for editing, (there are nested groups and components), Unhide All, and use the slider in the Soften Edges tray to soften. The result will also look better in shaded views.