Forge Viewer - Failing to load models randomally

I’m using Forge Viewer to load multiple models dynamically. After initializing the viewer with Autodesk.Viewing.Initializer, I iterate over my models and load them as follows:

models.forEach(model => {const documentId = 'urn:' + model.urn;
const applyRefPoint = model.applyRefPoint || false;
Autodesk.Viewing.Document.load(
  documentId,
  (viewerDocument) => {
    const defaultModel = viewerDocument.getRoot().getDefaultGeometry();
    const transformMatrix = viewerLoadInfo.forgeData.transform;

    const globalOffset = model.globalOffset || { x: 0, y: 0, z: 0 };

    let loadModelOptions = {
      keepCurrentModels: true,
      applyRefPoint,
      applyScaling: 'm',
    };

    viewer.loadDocumentNode(viewerDocument, defaultModel, loadModelOptions).then(onLoad);
  },
  (error) => {
    console.error(error);
  }
});

The code generally works, but sometimes, one or more models fail to load with the following error message:

Viewer3DImpl.js:5586 Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'isEmpty')
at te.hasModels (Viewer3DImpl.js:5586:30)
at ee.loadModel (Viewer3D.js:1539:24)
at D.loadModel (GuiViewer3D.js:324:48)

In Viewer3DImpl.js, the failing line of code is:

  /**
     * Whether any models have been loaded already.
     * A model is considered loaded as soon as the Model instance has
     * been added to RenderScene.
     */
    this.hasModels = function () {
        return !_renderScene.isEmpty();
    };

It seems like _renderScene is somehow undefined or uninitialized at the time this line runs. This error is intermittent, and sometimes the models load without any issue.

Has anyone encountered a similar issue with random load failures in Forge Viewer?

The render scene is setup as part of the Viewer3D#initialize method which is itself called within Viewer3D#start. Make sure you only start loading the models after viewer.start().