层添加子层vs层。插入子层动画

我正在制作一个动画

let gradientChangeAnimation = CABasicAnimation(keyPath: "colors")
    gradientChangeAnimation.duration = 5.0
    gradientChangeAnimation.toValue = [
        UIColor(red: 244/255, green: 88/255, blue: 53/255, alpha: 1).cgColor,
        UIColor(red: 196/255, green: 70/255, blue: 107/255, alpha: 1).cgColor
    ]
    gradientChangeAnimation.fillMode = kCAFillModeForwards
    gradientChangeAnimation.isRemovedOnCompletion = false
    gradientLayer.add(gradientChangeAnimation, forKey: "colorChange")

当我使用这种方法将其添加到视图中时,效果很好

self.view.layer.addSublayer(gradientLayer)

self.view.layer.insertSublayer(gradientLayer, at: 0)

但当我这样做时,动画完全停止工作

为什么会这样?