Navigation Buttons Lost in Storyboard App

I am trying to debug an iOS app which is using Storyboards. When the problem scene is first displayed it is correct, like so:

When I navigate through to the next scene by tapping one of the buttons such as "Any Category" and then navigate back again, the navigation buttons are gone like so:

I have not been able to find an obvious cause for this change. Is there something in particular I should be looking for that may be modifying the navigation bar? Perhaps there is some automatic handling by the storyboard process that needs to be disabled?

Here is part of the storyboard to provide context: