"WebMapServiceImageryProvider" The Resource is already being fetched

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

When I load WebMapServiceImageryProvider, I call the pickFeatures method and I get the "The Resource is already being fetched" error.

Later, I found that even if I didn't call the pickFeatures method and clicked on the globe multiple times, the "The Resource is already being fetched" error would appear.

2. A minimal code example. If you’ve found a bug, this helps us reproduce and repair it.
var world = new Cesium.WebMapServiceImageryProvider({
   url: ‘http://gisserver.tianditu.com/TDTService/gdp/2014/wms’,
   layers: ‘060101’,
   tileWidth: 256,
   tileHeight: 256,
   minimumLevel: 0,
   maximumLevel: 20,
var imageProvider = viewer.imageryLayers.addImageryProvider(world);

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

I need to get the data of the WMS ImageryLayerFeatureInfo at the current mouse click position and display it in a polygon.

4. The Cesium version you're using, your operating system and browser.
Version 1.51
Google Chrome

I can’t access the URL in your code, so I can’t test that. Are you able to reproduce this issue here?

Can you show how you’re using pickFeatures? Make sure you’re calling it after the ready boolean is true: