title: HERE Javascript API: Random Tile loading Errors
body: <p>I'm using the HERE Maps Javascript API to display a map in my Angular Website. 
  Most of the time it's working fine, but sometimes I'll get an error and the map does not render. </p>
  
  <p>This is the error:</p>
  
  <pre><code>mapsjs-core.js:369 Tangram [error]: Error for style group 'non-collision' for tile 15/9/263/170/9 Cannot read property 'retain' of undefined: TypeError: Cannot read property 'retain' of undefined
      at https://js.api.here.com/v3/3.1/mapsjs-core.js:369:259934
      at Array.forEach (&lt;anonymous&gt;)
      at https://js.api.here.com/v3/3.1/mapsjs-core.js:369:259905
      at ZoneDelegate.invoke (http://localhost:4200/polyfills.js:3365:26)
      at Object.onInvoke (http://localhost:4200/vendor.js:82817:33)
      at ZoneDelegate.invoke (http://localhost:4200/polyfills.js:3364:52)
      at Zone.run (http://localhost:4200/polyfills.js:3130:43)
      at http://localhost:4200/polyfills.js:3861:36
      at ZoneDelegate.invokeTask (http://localhost:4200/polyfills.js:3397:31)
      at Object.onInvokeTask (http://localhost:4200/vendor.js:82798:33)
  Jr @ mapsjs-core.js:369
  </code></pre>
  
  <p>This error seems to be random: If I just reload the page without making any changes, it will fail about 1 out of 10 times.
  The error can only be resolved with another page reload. </p>
  
  <p>This is how I add the map:</p>
  
  <pre><code>this.map = new H.Map(this.mapElement.nativeElement, tiles, {
      pixelRatio: window.devicePixelRatio || 1,
      center: { lat: this.lat, lng: this.lng },
  });
  
  const behavior = new H.mapevents.Behavior(
      new H.mapevents.MapEvents(this.map)
  );
  
  this.ui = H.ui.UI.createDefault(this.map, defaultLayers);
  this.ui.getControl('mapsettings').setVisibility(false);
  </code></pre>
  
  <p>I'm using both clustering and markers. I've tried to disable both of them, but the error still randomly appears. </p>
  
  <p>Does anybody have any idea? If you need more infos, please let me know.</p>