@tonycedeno It seems that a long time ago you had the same problem, since reviewing I see a similar post of yours.
https://community.cesium.com/t/errors-showing-kml-over-3d-tiles-mobile-view/10845
Interesting to see how Cesium ION improves visualization !!
I tested it on my Android Samsung S20+ and I can see how it fails in Sandcastle and fails less in Cesium ION, I would appreciate any tip to improve this in the community version of CesiumJS.
Can you please upload these assets to Cesium Ion and test it in another Sandcastle?
Best
Moses