Navigation Controller Embedded in Tab Controller - Tab Bar not visible

I have a Tab Bar Controller with 3 views embedded in it : 2 are normal ViewControllers and one is a Navigation Controller which has a ViewController with a CollectionView as in the picture below. Now when I first enter the Tab Bar Controller and navigate between the tabs, everything is fine. If I press any object in my collectionView, a new view gets pushed onto the navigationController. The problem occurs if I then press the back button and pop that view in order to return to the view containing the collectionView. In this situation, the tab bar on the bottom of the screen becomes invisible.