Hi Cesium Team, I am facing an issue, i am using pinBuilder() to create marker for Cluster and it is working fine on Ellipsoid Layer but whenever i used terrain layer its get faded and seems like going under the ground. So i checked your cesium sandcastle cluster example and i found that there is also same issue on terrain layer.
I created a video of that issue please have a look. it will help you more to find the issue.
This is because when you change to the Cesium World Terrain layer, viewer.scene.globe.depthTestAgainstTerrain is set to true. This causes some billboards to get occluded by the terrain.
To fix this, you can add an event listener that listens to when the terrain layer is changed (TerrainProviderChanged) and set the viewer.scene.globe.depthTestAgainstTerrain to false if the layer is Cesium World Terrain.