SKScene jitters/lags when a new SKSpriteNode is added - swift

Question

I'm constructing a Swift Playground with UIKit that contains an SKScene. After creating the code I'm planning to use within an Xcode project, I tried to adapt it into my Playground.
I encountered an issue while running the Playground - when a new SKSpriteNode is added to the Scene, the new and existing nodes jitter and lag for a split-second, then return to smooth 60fps. You can see this issue in effect here. No errors or warnings are spat, and the console is completely empty.
The scene in the project didn't have this issue, and I can't recreate it on another project - even when I directly copy-paste the code from the Playground to the project.
I searched the internet for answers to this issue and all I found was this StackOverflow question with no answers and the link to OP's supposed solution broken.
The code that is in effect for this SKScene is below.
class SimulatorController: UIViewController {
override func loadView() {
let view = SKView()
let scene = GameScene(size: view.bounds.size)
view.showsFPS = true
view.showsNodeCount = true
view.ignoresSiblingOrder = true
scene.scaleMode = .resizeFill
view.presentScene(scene)
self.view = view
}
}
class GameScene: SKScene {
override func didMove(to view: SKView) {
run(SKAction.repeatForever(SKAction.sequence([
SKAction.run(addNeutron),
SKAction.wait(forDuration: 1)
])
))
}
func random() -> CGFloat {
return CGFloat(Float(arc4random()) / 0xFFFFFFFF)
}
func random(min: CGFloat, max: CGFloat) -> CGFloat {
return random() * (max - min) + min
}
func addNeutron() {
let neutron = SKSpriteNode(imageNamed: "neutron.heic")
neutron.size = CGSize(width: 20, height: 20)
neutron.physicsBody = SKPhysicsBody(rectangleOf: neutron.size)
neutron.physicsBody?.isDynamic = true
let actualX = random(min: 0, max: size.width)
let actualY = random(min: 0, max: size.height)
neutron.position = CGPoint(x: actualX, y: actualY)
addChild(neutron)
let actualDuration = random(min: CGFloat(2.0), max: CGFloat(4.0))
let actualX2 = random(min: 0, max: size.width)
let actualY2 = random(min: 0, max: size.height)
let actionMove = SKAction.move(to: CGPoint(x: actualX2, y: actualY2), duration: TimeInterval(actualDuration))
let actionMoveDone = SKAction.removeFromParent()
neutron.run(SKAction.sequence([actionMove, actionMoveDone]))
}
}
Thanks so much for your help!