CMPT with I3DM's: features disappearing on map navigation

Hi, when zooming in to the tree in https://bertt.github.io/cesium_issues/cmpt_tree_disappears/tree_north/
the tree disappears:

tree_north

The tileset has a composite tile (0_0_0.cmpt), containing 2 I3dm models (one for the red box, one for the tree), each model has 1 instance.

Some more observations: