I spent way too long trying to work this out but couldn't find an answer. I'm definitely starting to feel like an idiot!
NavBar shows fine in edit mode and in preview mode, but for some reason once I either open the application in test more or in run mode, the navbar disappears. Similarly I tested out generating an APK and loading it on device - same outcome, it's not visible!
Any help greatly appreciated, I can't find any mention of this in the docs or video tutorials! Screenshots included below
Preview Mode
Test Mode
Page Navbar Settings
Navbar Settings
