I would like to highlight a bug with the new versione 1.16 of Cesium.
The terrain disappears at a certain level of zoom and tilting the camera near the terrain generates the same bug.
It seems that the issue is raised up only in certain areas, for example in the north east Italy.
To reproduce the bug search the city of "Trento" in the Cesium demo on the front page of the website.
I opened an issue on github with some animated gif: https://github.com/AnalyticalGraphicsInc/cesium/issues/3335
Thank you for the support.