Setting navigation item title issue.. why my navigation item seems many?

Question

I want to change the title of navigation bar but it seems somewhat confusing.. I did self.navigationItem.title = "ipsum" or self.navigationController?.navigationBar.topItem?.title = "ipsum" and so on.. but it fails..

It only succeeds changing the title when trying self.title = "ipsum" but it is not what I want because it causes tabBarItem's title to change too.

I tried debugging and found out strange result.

as you see the picture above.. there seems to be more than two navigationBar so when self.navigationItem.title = "ipsum" it actually changes some other or invisible navigationItem's title so that I can see from the log.

But the UI stays "lorem". Tell me if you figure something out! What am I missing?

EDIT 1:

Main.storyboard

Menu.storyboard

I put NavigationController in TabBarController and refactored NavigationController to another storyboard reference.

self.navigationItem.title = "ipsum" is called in the viewDidLoad() function.

Answer 1

Now View controllers are:

ViewController1 attached to item1:

override func viewDidLoad() {
        super.viewDidLoad()
        self.navigationItem.title="View1"

    }

ViewController2 attached to item2:

override func viewDidLoad() {
        super.viewDidLoad()
        self.navigationItem.title="View2"

    }

Result: