The diagram (storyboard) is a worry. Do you really mean to do what it says? There's a circle; that can't be right, surely.
Remember, when you use a segue, you are a creating a new instance of this view controller. So you are creating 2, then 3, then 4, then 5, then 6, and then another 2 on top of that in a potentially infinite loop of view controllers piling up.
Surely you want to do when you get to 6 is to unwind all the way back to 2. You want to remove 6, remove 5, remove 4, remove 3, leaving you back at 2.
Or perhaps you want a different instance of 2, to show on top of 6, but then it should be different, not the same one coming back from 6 in a loop. It is fine to have more than one instance of the same view controller in your storyboard, and they can be configured differently.