SpriteKit tunneling when user moves node - swift

Question

I have a question about (continuous) SpriteKit collision detection.
I have a SwiftUI/SpriteKit project in which balls fall from above and the user tries to catch the balls with a cup.
The user moves the cup horizontally by dragging their finger.
The physics work well with one exception -- the balls properly collide with each other, and with the cup, except when the cup is being moved.
When the cup is being moved by the user, the balls that had fallen into the cup tunnel right through the side of the cup.
Again, the balls collide with the cup correctly, and settle in the cup, except when the cup is moving.
EDIT: I added categoryBitMask and collisionBitMask to both the balls and the cup, as suggested in the comments. But the problem remains.
enum CollisionTypes: UInt32 {
case ball = 1
case cup = 2
}
The cup:
func cup() -> SKSpriteNode {
let screenSize = UIScreen.main.bounds
let cupNode = SKSpriteNode(imageNamed: "cup.png")
let cupNodeChild = SKSpriteNode(imageNamed: "cupOutline.png")
cupNode.position = CGPoint(x: screenSize.width*0.5, y: MainData.cupY)
cupNode.size = CGSize(width: screenSize.width * 0.25, height: screenSize.width * 0.35)
cupNode.name = "cup"
cupNode.zPosition = 1.0
cupNodeChild.size = CGSize(width: screenSize.width * 0.25, height: screenSize.width * 0.35)
cupNodeChild.name = "cupCollisionNode"
cupNodeChild.physicsBody = SKPhysicsBody(texture: cupNodeChild.texture!, size: CGSize(width: screenSize.width * 0.25, height: screenSize.width * 0.35))
cupNodeChild.physicsBody?.restitution = 0.0
cupNodeChild.physicsBody?.isDynamic = false
cupNodeChild.physicsBody?.usesPreciseCollisionDetection = true
cupNodeChild.physicsBody?.categoryBitMask = CollisionTypes.cup.rawValue
cupNodeChild.physicsBody?.collisionBitMask = CollisionTypes.ball.rawValue
cupNode.addChild(cupNodeChild)
return cupNode
}
The balls:
func initializeBalls(screenWidth: CGFloat, screenHeight: CGFloat) {
MainData.balls.removeAll()
for i in 0..<numOfBalls {
let radius = screenWidth * 0.02
let x = screenWidth * CGFloat.random(in: 0...1)
let y = screenHeight
let ballNode = SKSpriteNode(imageNamed: "ball.png")
ballNode.position = CGPoint(x: x, y: y)
ballNode.size = CGSize(width: radius*2, height: radius*2)
ballNode.name = "ball\(i)"
ballNode.physicsBody = SKPhysicsBody(circleOfRadius: radius)
ballNode.physicsBody?.usesPreciseCollisionDetection = true
ballNode.physicsBody?.mass = 5.0
ballNode.physicsBody?.isDynamic = true
ballNode.physicsBody?.categoryBitMask = CollisionTypes.ball.rawValue
ballNode.physicsBody?.collisionBitMask = CollisionTypes.cup.rawValue
ballNode.physicsBody!.contactTestBitMask = ballNode.physicsBody!.collisionBitMask
ballNode.physicsBody?.restitution = 0.1
MainData.balls.append((
x: x,
y: y,
radius: radius,
img: "ball.png",
node: ballNode
))
}
}
Here's how I move the cup, in my GameScene:
func touchMoved(toPoint pos : CGPoint) {
let action = SKAction.move(to: CGPoint(x: pos.x, y: MainData.cupY), duration: 0)
cupNode?.run(action)
}
Why is this tunneling happening, and how do I avoid it?