I have this problem when I am running a background thread that uses "self" to look for variables with specific names. The project crashes and says that I cant make any enumerations on the "NSArray" which I searched up, and found out that is a list of all the objects in the scene which can't be edited. So I made this dummy project to show my problem in a simpel way. Here is the code: import SpriteKit import Foundation class GameScene: SKScene{ override func sceneDidLoad() { } var boxArray = [String]() var boxNumber = 1 func addBox(){ var box = SKSpriteNode() box.size = CGSize(width: 100, height: 100) box.color = SKColor.red box.position = CGPoint(x: 0, y: 0) box.name = "box\(boxNumber)" self.addChild(box) boxArray.append(box.name!) boxNumber += 1 } func moveBox(){ for i in boxArray{ if self.childNode(withName: "\(i)") != nil{ var box = self.childNode(withName: "\(i)") as! SKSpriteNode box.position.x += 10 } } } override func touchesBegan(_ touches: SetUITouch, with event: UIEvent?) { addBox() } override func update(_ currentTime: TimeInterval) { DispatchQueue.global(qos: .background).async { self.moveBox() } } Here is the crash report 2021-05-07 20:06:12.568267+0200 threading[99375:16974860] Metal GPU Frame Capture Enabled 2021-05-07 20:06:12.568677+0200 threading[99375:16974860] Metal API Validation Enabled IPHONE 2021-05-07 20:06:18.951497+0200 threading[99375:16975092] * Terminating app due to uncaught exception 'NSGenericException', reason: '* Collection __NSArrayM: 0x283018060 was mutated while being enumerated.' * First throw call stack: (0x18d09d9d8 0x1a1406b54 0x18d09d39c 0x1bf463c90 0x1bf463480 0x1bf462ecc 0x1bf462e10 0x102fcc50c 0x102fcca08 0x102fcca4c 0x103733ce4 0x103735528 0x1037471e4 0x103747970 0x1d5743568 0x1d5746874) 2021-05-07 20:06:18.954714+0200 threading[99375:16975088] * Terminating app due to uncaught exception 'NSGenericException', reason: '* Collection __NSArrayM: 0x283018060 was mutated while being enumerated.' * First throw call stack: (0x18d09d9d8 0x1a1406b54 0x18d09d39c 0x1bf463c90 0x1bf463480 0x1bf462ecc 0x1bf462e10 0x102fcc380 0x102fcca08 0x102fcca4c 0x103733ce4 0x103735528 0x1037471e4 0x103747970 0x1d5743568 0x1d5746874) libc++abi.dylib: terminating with uncaught exception of type NSException * Terminating app due to uncaught exception 'NSGenericException', reason: '* Collection __NSArrayM: 0x283018060 was mutated while being enumerated.' So the function "moveBox" is being ran in the background thread which is all fine and it works. But by making a new SKSpritenode I will have made a change in the NSArray by inserting a new element, therefor the app crashes. How can I make a new SKSpriteNode, use the background thread and call a node from "self" all the same time without the app crashing? I appreciate all the help i can get.