Loading scene created from Reality Composer cannot be reused

I created a scene in Reality Composer which includes lots of different models. Then I load scene and try to load model and place them separately, the following is my UITapGestureHandler:

guard let loadModel = loadedScene.findEntity(named: selectedPlant.selectedModel)
            else{
                return
 } 
loadModel.setPosition(SIMD3(0.0,0.0,0.0), relativeTo: nil)

My confusion is, when you use .findentity and place this model to the detected plane, it cannot be retrieved again: I try to call this again to place a second model after placing the first one, and .findentity returns nil. Does anyone know the mechanism behind it? I thought loading the scene will create a template in memory, but in contrary, it seems like only creating a sort of list and pop out entity for every call.