Left swipe to go back is disabled by Apple in this mode:
We didn’t design Discourse to be used without the browser back-button, so we disabled the feature for now, like Starbucks in the example above.
Android doesn’t have this problem because a back button is permanent in either the OS UI or in the form of a physical back button.
We are always happy to discuss and re-evaluate, but the situation is kinda messy in iOS.