CesiumTerrainProvider don't send net request for terrain tiles when map zoom level changed

1. A concise explanation of the problem you’re experiencing.

2. A minimal code example. If you’ve found a bug, this helps us reproduce and repair it.

var viewer = new Cesium.Viewer(‘cesiumContainer’);

// Load ArcticDEM terrain

var cesiumTerrainProviderMeshes = new Cesium.CesiumTerrainProvider({

url : ‘http://192.168.98.201:10050’,

requestWaterMask : true,

requestVertexNormals : true

});

viewer.terrainProvider = cesiumTerrainProviderMeshes;

When map zoom level great than 3,cesium never request new terrain tiles;

terrain server environment:

OS: ubuntu 16.4

web server: apache 2 ;

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you’re using, your operating system and browser.