SceneKit Animations Transition Abruptly on iOS 18 Device, but Smooth in Simulator

Hi Friends! I’m facing an issue with SceneKit.

I’m developing a 3D mobile game. I have a character 3D model and several skeletal animations CAAnimation. I import both the model and the animations from Maya in *.dae format. The character’s animations play continuously one after the other, with each new animation being triggered randomly. The transition between animations makes smoothly by setting the fadeInDuration and fadeOutDuration properties. Here’s an example of the code:

import UIKit import QuartzCore import SceneKit

class TestAnimationController: UIViewController {

var bodyNode: SCNNode?  

override func viewDidLoad() {
    super.viewDidLoad()
    
  let scnView = SCNView(frame: self.view.bounds)
  scnView.backgroundColor = .black // Set your desired background color
  scnView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
  
  let scene = SCNScene(named: "art.scnassets/scene/Base_room/ROOM5.scn")!
  bodyNode = collada2SCNNode(filepath: "art.scnassets/female/girl_body_races.dae")!
  bodyNode?.renderingOrder = 10
  
  scene.rootNode.addChildNode(bodyNode!)

  playIdleAnimation()
  
  scnView.scene = scene // Assign the scene to the SCNView
  self.view.addSubview(scnView) // Add the SCNView to your main view)
}
func collada2SCNNode(filepath:String) -> SCNNode? { if let scene = SCNScene(named: filepath) { let node = scene.rootNode.childNodes[0] return node } else { return nil } }

func playIdleAnimation() {
    let array = [
        "art.scnassets/female/animations/idle/girl_idle_4.dae",
        "art.scnassets/female/animations/idle/girl_idle1.dae",
        "art.scnassets/female/animations/idle/girl_idle2.dae",
        "art.scnassets/female/animations/idle/Girl_idle3.dae",
    ]
    let animation =  CAAnimation.animationWithSceneNamed(array.randomElement() ?? "")!
    self.setAnimationAdd(
      fadeInDuration: 1.0,
      fadeOutDuration: 1.0,
      keyTime: 0.99,
      animation,
      isLooped: false
    ) { [weak self] in
      guard let self = self else { return }
      try? self.playBoringAnimations()
    }
}

func playBoringAnimations() {
    let array = [
        "art.scnassets/female/animations/boring/girl_boring1.dae",
        "art.scnassets/female/animations/boring/girl_boring2.dae",
        "art.scnassets/female/animations/boring/girl_boring3.dae",
        "art.scnassets/female/animations/boring/girl_boring4.dae",
        "art.scnassets/female/animations/boring/girl_boring5.dae",
        "art.scnassets/female/animations/boring/girl_boring6.dae",
        "art.scnassets/female/animations/boring/girl_boring8.dae"
    
    ]
    let animation =  CAAnimation.animationWithSceneNamed(array.randomElement() ?? "")!
    self.setAnimationAdd(
      fadeInDuration: 1.0,
      fadeOutDuration: 1.0,
      keyTime: 0.99,
      animation,
      isLooped: false
    ) { [weak self] in
      guard let self = self else { return }
      try? self.playIdleAnimation()
    }
}


func setAnimationAdd(fadeInDuration : CGFloat, fadeOutDuration : CGFloat, keyTime : CGFloat,  _ animation: CAAnimation, isLooped: Bool, completion: (() -> Void)?) {
    
    animation.fadeInDuration = fadeInDuration
    animation.fadeOutDuration = fadeOutDuration
  
    if !isLooped {
        animation.repeatCount = 1
    } else {
        animation.repeatCount = Float.greatestFiniteMagnitude
    }
    animation.animationEvents = [
        SCNAnimationEvent(keyTime: keyTime, block: { _, _, _ in completion?() })
    ]
    bodyNode?.addAnimation(animation, forKey: "avatarAnimation")
}
}

Everything worked perfectly until I updated to iOS 18. On a physical device, the animations now transition abruptly without the smooth blending that was present in earlier iOS versions. The switch between them is very noticeable, as if the fadeInDuration and fadeOutDuration parameters are being ignored.

However, in the iOS 18 simulator, the animations still transition smoothly as before.

Here two example videos - IOS 17.5 and IOS 18 https://youtube.com/shorts/jzoMRF4skAQ - IOS 17,5 smooth https://youtube.com/shorts/VJXrZzO9wl0 - IOS 18 not smooth

I try this code in IOS 17.5, everything works fine Does anyone have any ideas on how to fix this issue?