UILabel Attributed Text Anomaly: Unexpected Strikethrough When Setting Text Property in Swift

The following code, will create a red color text, without strike-through.

class ViewController: UIViewController {

    @IBOutlet weak var label: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let text = "Hello World"
        let textCount = text.count
        let fullRange = NSRange(location: 0, length: textCount)
        
        var attributedText = NSMutableAttributedString(string: text)
        attributedText.addAttribute(.foregroundColor, value: UIColor.green, range: fullRange)
        attributedText.addAttribute(.strikethroughStyle, value: NSUnderlineStyle.single.rawValue, range: fullRange)
        label.attributedText = attributedText
        
        attributedText = NSMutableAttributedString(string: text)
        attributedText.addAttribute(.foregroundColor, value: UIColor.red, range: fullRange)
        attributedText.removeAttribute(NSAttributedString.Key.strikethroughStyle, range: fullRange)
        label.attributedText = attributedText
    }
}

However, if I trigger label.text in between, it will cause the following strange behavior : A red color text, with strike-through created at the end of function.

class ViewController: UIViewController {

    @IBOutlet weak var label: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let text = "Hello World"
        let textCount = text.count
        let fullRange = NSRange(location: 0, length: textCount)
        
        
        var attributedText = NSMutableAttributedString(string: text)
        attributedText.addAttribute(.foregroundColor, value: UIColor.green, range: fullRange)
        attributedText.addAttribute(.strikethroughStyle, value: NSUnderlineStyle.single.rawValue, range: fullRange)
        label.attributedText = attributedText
        
        // Why this will cause a red color text, with strike-through created at the end of function?
        label.text = text
        
        attributedText = NSMutableAttributedString(string: text)
        attributedText.addAttribute(.foregroundColor, value: UIColor.red, range: fullRange)
        attributedText.removeAttribute(NSAttributedString.Key.strikethroughStyle, range: fullRange)
        label.attributedText = attributedText
    }
}

Does anyone what is the reason behind this behavior, and how I can avoid such? Thank you.