multiline UILabel using AttributedText with lineSpacing is adding unwanted offset on iphone 6+ & 7+

Question

I have a UILabel with attributed text that includes specific lineSpacing or lineHeightMultiple.

let titleParagraphStyle = NSMutableParagraphStyle()
//titleParagraphStyle.lineSpacing = lineSpacing
titleParagraphStyle.lineHeightMultiple = 1.5
titleParagraphStyle.alignment = .left

let titleAttributes = [NSForegroundColorAttributeName: color,
                                   NSFontAttributeName: UIFont(name: fontName, size: fontSize)!,
                                   NSParagraphStyleAttributeName : titleParagraphStyle] as [String : Any]

let titleAttrString = NSAttributedString(string:string, attributes: titleAttributes)

var label = BetterUILabel() 
label.numberOfLines = 0       
label.attributedText = titleAttrString
label.setNeedsLayout() //I'm trying everything
label.layoutIfNeeded()
label.sizeToFit()

The BetterUILabel is a subclass of UILabel with fixes for perferredMaxLayoutWidth

class BetterUILabel: UILabel {

    override public func layoutSubviews(){
        super.layoutSubviews()
        self.preferredMaxLayoutWidth = self.bounds.width
        super.layoutSubviews()
    }

    override public var bounds: CGRect
        {
        didSet
        {
            self.preferredMaxLayoutWidth = self.bounds.width
        }
    }

    override public var frame: CGRect
        {
        didSet
        {
            self.preferredMaxLayoutWidth = self.frame.width
        }
    }

}

label is a subview of a uiView which is a arranged view of a vertical UIStackView within a UIScrollView.

The label is pinned to the top, left, and right of it's superview. It relies on it's intrinsic content size to drive it's height. If I remove any lineSpacing or lineHeightMultiple from the style or use regular non-attributed text, it sizes nicely. However, with those attributes, it is sometimes cutting off the last line on 6+ and 7+ devices.

I've exaggerated the line spacing to show the issue.

With the orange background the UILabel is working on a 6:

On the 6+, with the green background, the UILabel appears to have vertical space at the top which is causing the text to truncate:

What causes this. Is there a fix to this issue?