How to update UILabel text in custom class after initialization (Swift 3)

I have custom UIStackView class but after initialization I cannot change labels in it, because its referring to different label objects.

//  ViewBlocksController.swift
//  player

import UIKit

let nowPlayingControl = NowPlayingController()

@IBDesignable class TitlesFrame: UIStackView {
    //Labels variables
    let songTitle = UILabel()
    let artistAlbumTitle = UILabel()

    //Initialization
    override init(frame: CGRect) {
        super.init(frame: frame)
        arrangeView()
    }

    required init(coder: NSCoder) {
        super.init(coder: coder)
        arrangeView()
    }

    func arrangeView(){
        //Get initial text
        (songTitle.text, artistAlbumTitle.text) = nowPlayingControl.getTitles()

        //Add labels to the stack
        addArrangedSubview(artistAlbumTitle)
        addArrangedSubview(songTitle)

        //Test what label is used
        print(songTitle)
    }

    func updateTitles(){
        (songTitle.text, artistAlbumTitle.text) = nowPlayingControl.getTitles()
    }
}

I call updateTitles() from my MainViewController class:

//  MainViewController.swift
//  player

import UIKit

class MainViewController: UIViewController {

    let titlesFrame = TitlesFrame()

    //Will call this on custom notification
    func callUpdate(){
        titlesFrame.updateTitles()
    }
}

Print gives me following objects:

<**UILabel: 0x100c15b90**; frame = (0 0; 0 0); text = 'Unknown Artist
\342\200— Unknown ...'; userInteractionEnabled = NO; layer =
<_UILabelLayer: 0x1700956d0>>

<**UILabel: 0x100d19d90**; frame = (0 0; 0 0); text = 'Unknown Artist —
Unknown ...'; userInteractionEnabled = NO; layer = <_UILabelLayer:
0x174097f70>>

When I try to update labels with updateTitles() method, it always update 1st object (UILabel: 0x100c15b90). But Storyboard instead displays 2nd object (UILabel: 0x100d19d90) and it is never updated.

How can I update labels on Storyboard?