UIView animation causing label to twitch - ios

Question

I have an IconView class that I use as a custom image for a Google Maps marker. All of the print statements show that the code is correctly executing. However, the "12:08" UILabel in circleView keeps on growing and shrinking (i.e. twitching). I can't figure out what the problem might be. I've tried manually setting the the font in the completion block, commenting out the adjustsFontSizeToFitWidth, changing the circleView to a UIButton.
import UIKit
class IconView: UIView {
var timeLabel: UILabel!
var circleView: UIView!
var clicked: Bool!
//constants
let circleViewWidth = 50.0
let circleViewHeight = 50.0
override init(frame:CGRect) {
super.init(frame : frame)
self.backgroundColor = UIColor(red: 47/255, green: 49/255, blue: 53/255, alpha: 0.0)
clicked = false
if !clicked {
//MAIN CIRCLE
print("init circle view")
circleView = UIView(frame: CGRect(x:0, y:0, width:circleViewWidth, height:circleViewHeight))
circleView.backgroundColor = UIColor(red: 47/255, green: 49/255, blue: 53/255, alpha: 1.0)
circleView.layer.cornerRadius = circleView.frame.size.height / 2.0
circleView.layer.masksToBounds = true
self.addSubview(circleView)
timeLabel = UILabel(frame: CGRect(x: 0, y: 0, width: circleViewWidth, height: circleViewHeight/3.0))
timeLabel.center = circleView.center
timeLabel.text = "12:08"
timeLabel.textAlignment = .center
timeLabel.textColor = .white
timeLabel.numberOfLines = 0
timeLabel.font = UIFont.systemFont(ofSize: 11)
timeLabel.font = UIFont.boldSystemFont(ofSize: 11)
timeLabel.adjustsFontSizeToFitWidth = true
circleView.addSubview(timeLabel)
}
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
}
func mapView(_ mapView: GMSMapView, didTap marker: GMSMarker) -> Bool {
let iconView = marker.iconView as! IconView
print("going to start animating")
if !iconView.clicked {
UIView.animate(withDuration: 0.2, animations: {
print("making this bigger now")
iconView.circleView.transform = CGAffineTransform(scaleX: 1.2, y: 1.2)
})
{ (finished:Bool) -> Void in
print("DONE")
iconView.clicked = true
}
}
return true
}