I think related to the quirky https://github.com/CesiumGS/cesium-ion-rest-api-examples/issues/291
I threw some historical aerial photos through photogrammetry software. Tileset Locating after model upload was difficult as the model kept vanishing when zooming out and I struggled to get oriented.
I have added the aerials to the second slide of the story from the GitHub link - https://cesium.com/ion/stories/viewer/?id=24df180f-8dbf-4297-b4eb-af881394ce82 - they also vanish when zooming out.
I thought to mention it here in case anyone else is having this issue.
For improved tileset locating I wonder about the ability to adjust model transparency.