Nick, you are a great plugin producer, let me start with that. Thanks for your patience as I deploy your sections/plugins across my network. So, I've used the navable plugin on two separate sites now, on one, it is working perfectly (ecd.transformecommunications.com) but on the other (redwoodpark.ca/home) it isn't working at all. The only differences between the two that I can think of is that the second site is running WP Multisite and content was imported from another site, menus included. I've gone in and set the menu in the menus area and also saved the menu as well in case that was an issue.
I can't think of why I might be getting this issue on one site but not the other.