How to remove shadow area at the rear part of 3Dtile

CesiumJS
1

Shadow area appears at the rear part of 3Dtile
Could you tell me haw to remove it.

My cesium is v1.54.

The code is as follows:
It is very simple.

<!DOCTYPE html>
<html lang="en">
<head>
  <!-- Use correct character set. -->
  <meta charset="utf-8">
  <!-- Tell IE to use the latest, best version. -->
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <!-- Make the application on mobile take up the full browser screen and disable user scaling. -->
  <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
  <title>TEST</title>
  <script src="./Cesium/Cesium.js"></script>
  <style>
      @import url(./Cesium/Widgets/widgets.css);
      html, body, #cesiumContainer {
          width: 100%; height: 100%; margin: 0; padding: 0; overflow: hidden;
      }
  </style>
</head>
<body>
  <div id="cesiumContainer"></div>
  <script>

    var viewer = new Cesium.Viewer('cesiumContainer');
    var tileset = viewer.scene.primitives.add(new Cesium.Cesium3DTileset({
    url : './Tileset_022603/tileset.json',
    }));

    viewer.zoomTo(tileset)

  </script>
</body>
</html>

2

Can you post a screenshot of what you’re seeing? Shadows on models aren’t enabled by default.

Does the shadow move when you move the timeline at the bottom?