Missing geometry on scene-viewer

### Description

When loading [this model](
https://shapediverviewer.s3.amazonaws.com/v3/gltf/example.gltf) in the scene-viewer, parts of the geometry is missing. It should be three planes and three cubes, but only the three planes are visible. The GLTF seems to be in order, no issues when I check the model details on https://gltf-viewer.donmccurdy.com/. This does not happen in WebXR or when the scene-viewer was created via the model-viewer (with this page at least https://modelviewer.dev/editor/).

Is there a difference in how I load the scene-viewer compared to the example below? I couldn't find anything.

#### Live Demo

A very easy CodeSandBox to reproduce the issue:
https://codesandbox.io/s/6rrwto

The model (three cubes and three planes):
https://shapediverviewer.s3.amazonaws.com/v3/gltf/example.gltf

It works when I load the same model on the [model-viewer editor](https://modelviewer.dev/editor/) and select "Default AR Mode to Scene Viewer". I looked at the code of the model-viewer and how the scene-viewer is loaded there and I could not find a difference.

### Version
scene-viewer 1.0 / 1.1

### Browser Affected
-

### OS
- [ X ] Android
- [ ] iOS
- [ ] Linux
- [ ] MacOS
- [ ] Windows

### AR
- [ ] WebXR
- [ X ] SceneViewer
- [ ] QuickLook