SpriteKit - Collision detection not working - ios

Question

i've got a problem with the collisions.
adding physicbody depending on tilemap:
guard let tilemap = childNode(withName: "LevelGround") as? SKTileMapNode else { return }
let tileSize = tilemap.tileSize
let halfWidth = CGFloat(tilemap.numberOfColumns) / 2.0 * tileSize.width
let halfHeight = CGFloat(tilemap.numberOfRows) / 2.0 * tileSize.height
for row in 0..<tilemap.numberOfRows {
for col in 0..<tilemap.numberOfColumns {
if tilemap.tileDefinition(atColumn: col, row: row) != nil {
let x = CGFloat(col) * tileSize.width - halfWidth
let y = CGFloat(row) * tileSize.height - halfHeight
let rect = CGRect(x: 0, y: 0, width: tileSize.width, height: tileSize.height)
let tileNode = SKShapeNode(rect: rect)
tileNode.position = CGPoint(x: x, y: y)
tileNode.physicsBody = SKPhysicsBody(rectangleOf: tileSize, center: CGPoint(x: tileSize.width / 2.0, y: tileSize.height / 2.0))
tileNode.physicsBody?.isDynamic = false
tileNode.physicsBody?.affectedByGravity = false
tileNode.physicsBody?.collisionBitMask = Physics().player | Physics().bullet
tileNode.physicsBody?.categoryBitMask = Physics().ground
tileNode.physicsBody?.contactTestBitMask = Physics().ground | Physics().player
tileNode.physicsBody?.friction = 0.1
tileNode.physicsBody?.restitution = 0
tileNode.strokeColor = .white
tileNode.name = "Ground"
self.world.addChild(tileNode)
}
}
}
Let the bullet spawn on tapping the action2 button:
if self.ctrlAction2.contains(touch.location(in: cam)) {
let bullet = SKShapeNode(ellipseOf: CGSize(width: 5, height: 4))
bullet.fillColor = .orange
bullet.physicsBody = SKPhysicsBody(edgeLoopFrom: bullet.path!)
bullet.physicsBody?.affectedByGravity = true
bullet.physicsBody?.categoryBitMask = Physics().bullet
bullet.physicsBody?.collisionBitMask = Physics().enemy | Physics().ground
bullet.physicsBody?.contactTestBitMask = Physics().bullet | Physics().enemy | Physics().ground
bullet.position.y = charakter.position.y + charakter.size.height / 7
bullet.physicsBody?.isDynamic = true
bullet.name = "bullet"
if facing == "right" {
bullet.position.x = charakter.position.x + charakter.size.width / 1.9
self.world.addChild(bullet)
bullet.run(SKAction.moveBy(x: 2000, y: 0, duration: 4))
} else if facing == "left" {
bullet.position.x = charakter.position.x - charakter.size.width / 1.9
self.world.addChild(bullet)
bullet.run(SKAction.moveBy(x: -2000, y: 0, duration: 4))
}
}
The bullet collides with enemies, the enemies collides with the player and the player collides with the ground - everything works, except the collision between bullet and ground.
Thank you for your help in advance
Pascal