SKEmitterNode animation along path - lag / space after start - Swift

Hi All,
I create some application, where I draw some lines using SKEmitterNode animation with big value sparkEmmiter.particleBirthRate = 500 for smooth drawing. Unfortunately, here is some strange effect after start animation - some space between first particle emitters and all others - example: o[space]oooooo - tested on iPhone 5s. What I know only, that problem is on sparkEmmiter.particleScaleSpeed = 0.3, when I set 0, then it seems OK, but I need this.

Please, could You help me with this?
Do you have some experience with this?

override func touchesBegan(_ touches: Set, with event: UIEvent?) {
let mySprite = SKSpriteNode()
mySprite.position = CGPoint(x: 50, y: 50)
mySprite.size = CGSize(width: 45, height: 45)
self.addChild(mySprite)

let sparkEmmiter = SKEmitterNode()
let image = UIImage(named:“spark.png”)!
sparkEmmiter.particleTexture = SKTexture(image: image)
sparkEmmiter.particleColor = SKColor.red
sparkEmmiter.particleBirthRate = 500
sparkEmmiter.particleLifetime = 1.25
sparkEmmiter.particleAlpha = 1
sparkEmmiter.particleAlphaSpeed = -0.8
sparkEmmiter.particleScale = 0.1
sparkEmmiter.particleScaleSpeed = 0.6
sparkEmmiter.particleColorBlendFactor = 4
sparkEmmiter.particleBlendMode = SKBlendMode.alpha
sparkEmmiter.particleColorSequence = nil
sparkEmmiter.targetNode = self

let circle = UIBezierPath(arcCenter: CGPoint(x: self.frame.midX,y: self.frame.midY), radius: CGFloat(200), startAngle: CGFloat(0), endAngle:CGFloat(Double.pi * 2), clockwise: true)

let followTrack = SKAction.follow(circle.cgPath, asOffset: false, orientToPath: true, duration: 1.25)
let followTrackForever = SKAction.repeatForever(followTrack)
mySprite.run(followTrackForever)
mySprite.addChild(sparkEmmiter)
}