为什么地球放大加载清晰后加载的kml文件模型就消失看不见了,好像只有地球没有加载到最底层模糊层面时才会显示出来,这个是什么情况??

代码片段:
let f = document.getElementById("inputfile");
      f.addEventListener("change", (evt) => {
        let target = evt.target;
        let file = target.files[0];
        if (!file) return;
        Winviewer.dataSources.add(
            Cesium.KmlDataSource.importFile(file, {
              camera: Winviewer.scene.camera,
              canvas: Winviewer.scene.canvas,
            })
          )
          .then((dataSource) => {
            Winviewer.flyTo(dataSource);
            Winviewer.scene.layer = dataSource;
          });
      });