Question FaceTracking issue on IOS when Reloading Scene

The issue I'm Facing is when reloading the scene again face tracking is not working. it's only happening on IOS in android it works well.

consider scenario :
I've two scenes 1) 3D scene and 2)Facetracking scene(mars)

when I'm changing the scene from 1st scene to 2nd scene FaceTracking works well for the first time. but after that reloading, the 2nd scene again face tracking not working. It's also not working If I load 1st scene and then loading 2nd scene.