Hi Brad, the NCX template doesn't match what we've done to support invisible parts. See [here](https://github.com/pressbooks/pressbooks/blob/90edbf48ee394d4de9f91a43a3bf98f10bbb065f/includes/modules/export/epub/templates/ncx.php#L47-66). Basically, if the part is invisible, any chapters that are within it appear at the top level of the NCX hierarchy and therefore don't appear to have a parent part in exports. Let me know if this makes sense.