ARKit and RealityKit limitation Entity number - swift

Question

I am study RealityKit and I'm try to drop on the floor a set of red card divided in different row at the position tapped.
See the picture attached.
I notice that if the number of cards is to much AR kit display the cards for few second in the sene but then after a second the cards disappeared from a scene.
and on the console I get the following print out:
2021-10-10 15:31:31.851724+0800 indovinaWho[12166:4021700] [Session] ARSession <0x111038050>: ARSessionDelegate is retaining 14 ARFrames. This can lead to future camera frames being dropped.
Here my code how I drop the cards.
Basically with the following code I'm creating a AnchorEntity at location tapped and then append the entity "modCard" changing the position accordingly.
If for example I state 8 card per row in 3 row, I just see the card for few second and then suddently they disappeared from my scene.
Reality kit have a maximum number of entity can be attached to an AnchorEntity?
func createCard(raycast: ARRaycastResult, maxrow: Int, cardPerRow: Int){
let anchor = AnchorEntity(raycastResult: raycast)
var prPosMod = simd_make_float3(0,0,0) // prev position
let cardByside = cardPerRow/2
DispatchQueue.global().sync {
for _ in 1...maxrow {
for ncard in 1...cardPerRow {
let modEntity = self.modelCard()
if ncard < cardByside {
modEntity.position = simd_make_float3(prPosMod.x-0.1,prPosMod.y,prPosMod.z)
}else {
modEntity.position = simd_make_float3(prPosMod.x + 0.1,prPosMod.y,prPosMod.z)
}
prPosMod = modEntity.position
anchor.addChild(modEntity)
}
prPosMod = simd_float3(0,prPosMod.y,prPosMod.z-0.1)
}
self.arView.scene.addAnchor(anchor)
}
}
func modelCard() -> ModelEntity {
let mesh = MeshResource.generateBox(width: 0.08, height: 0.01, depth: 0.08, cornerRadius: 0.005, splitFaces: false)
let material = SimpleMaterial(color: .red, isMetallic: false)
return ModelEntity(mesh: mesh, materials: [material])
}