The problem is that when tiling models like this Cesium ion does not currently take into account any projection information. So in this case, the ideal solution is to be able to say that the coordinates of this model are in some specific projection, so the geometry is interpreted to be at a fixed height from the surface as opposed to just an absolute position in space relative to one model origin.
This is something we're currently working on improving. Can you let me know what the asset ID for this asset is? That'll help us look into making sure we can support use cases like this.