ShadowMap visibility on personal 3dTiles

Hi to all!

I’m trying to implement something similar to viewshed analysis on our own textures.
I succeeded to create the example using the following ShadowMap project on cesium OSM 3dtileset (Sandcastle link)

however, when I’m trying my own 3dTiles asset (loaded from cesium Ion), the building are being loaded properly and presented in the map, but the shadow calculation returns nothing (the entire visibility color is red), what could be the issue? should we add some properties to the textures in order to make this feature work?

Cesium OSM 3dTiles result:

Our 3dTiles result:

any help would be greatly appreciated

Can you share full source code of this project ?