Edit 21/08/25:
Like mentioned below turning on alpha clipping instead of changing the surface type works too and prevents certain artifacts.
I have managed to find the issue!
Its actually rather dumb and simple… the default material inside the package isn’t set to transparent but opaque. you need to make a copy of CesiumUnlitTilesetMaterial, change the surface type from opaque to transparent and turn of Preserve specular lighting and assign it on the 3D Tileset.
