I3dm not rendering model

Hi.

I am trying to create an instanced 3d model tile set but cannot get my model (a basic cube for now) to render. I am not seeing any errors just nothing loading.

The cesium validator claims my i3dm file is valid but nothing displays.

The file currently contains a single location. that should render in the lower left corner of the bounds defined in the tile set json file

ion asset id is 853413

Thanks