Use UIFontDescriptor
I was having the same issue on iOS 13. Fixed it by using fontDescriptor instead of fontName. I have UILabel in my storyboard connected to its view controller via IBOutlet with font as Text Styles - Callout.
@IBOutlet weak var lblText: UILabel!
Below one didn't worked as expected and showing Times New Roman font:
let font = UIFont.init(name: lblText.font.fontName, size: 50.0)!
lblText.font = font
lblText.text = "Times Coding :)"
Solution using UIFontDescriptor:
let font = UIFont.init(descriptor: lblText.font.fontDescriptor, size: 50.0)
lblText.font = font
lblText.text = "Times Coding :)"
This way it will pick the font you set to a label in your storyboard, you don't need to hardcode the font name.