Can you put together a Sandcastle example showing this problem? It’d help to be able to reproduce it so I can figure out if it’s a problem with Cesium, or with the data etc.
The issue at #5984 has just been closed and may resolve your issue. Look for the change in the Cesium 1.48 release on August 1st, or get it now in the master branch on GitHub https://github.com/AnalyticalGraphicsInc/cesium.