Hi Don!
I have limited exposure to the mobile app, so your question really gave me the push to install the app and get it working with my Moodle sites.
I tried it first on my personal sandpit site - Moodle.Scott.Technology. I had recently upgraded this site to 3.3, and with 3.3 you can't even orphan activities any more, they're all just stealth activities. I knew your site isn't 3.3, so I quit playing with it to try to get something closer to your situation.
(As a side note, I love the language here. The latest version of Moodle has no orphans. Ha!)
I set up the Mobile app with this site, and took a look at this current course as a student in the app. And my results were the same as yours - I could see topics 6 & 7, which are orphaned.
I don't know if there's a way around this.
If anyone knows, I'd love to hear solutions! Please feel free to comment. I'll keep asking around too.
- Scott
(And as another aside - learn.pukunui.com is now Mobile App enabled!)