I have a collada file containing the model for a house (without the sides). When I convert it to glTF most of the solar panels and the back half of the roof is not shown in cesium.
The collada model:
the glTF model (converted from collada):
I have uploaded the collada file to this url so you can download it: https://www.dropbox.com/s/z13blnq3w7libbz/model.zip?dl=0
The resulting glTF file can be found via this url: https://www.dropbox.com/s/0hopzzhb5l9204w/model_gltf.zip?dl=0