问为什么带有` `didRemove [ARAnchor]`的`session`方法没有调用`ARBodyTrackingConfiguration`？

EN

import ARKit
import RealityKit
import UIKit

class AugmentedVideoView: ARView, ARSessionDelegate {
    func session(_ session: ARSession, didAdd anchors: [ARAnchor]) {
        print("didAdd") // called correctly
    }

    func session(_ session: ARSession, didUpdate anchors: [ARAnchor]) {
        print("didUpdate") // called correctly
    }

    func session(_ session: ARSession, didRemove anchors: [ARAnchor]) {
        print("didRemove") // is never called :-(
    }

    required init(frame: CGRect) {
        #if targetEnvironment(simulator)
        super.init(frame: frame)
        handleError("Camera not available in simulator.")
        return

        #else
        super.init(frame: frame,
                   cameraMode: ARView.CameraMode.ar,
                   automaticallyConfigureSession: false)
        self.session.delegate = self

        guard ARBodyTrackingConfiguration.isSupported else {
            handleError("Your device does not support body tracking.")
            return
        }

        let configuration = ARBodyTrackingConfiguration()
        configuration.automaticSkeletonScaleEstimationEnabled = false
        self.session.run(configuration)
        #endif
    }

    @available(*, unavailable)
    dynamic required init?(coder decoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}