Can you clarify what you mean by “height”? Cesium for Unreal uses the WGS84 ellipsoid model, and in the Longitude Latitude Height coordinate model, “height” refers to the height above the ellipsoid. This is often not equal to the height above sea level.
These forum threads aren’t exactly the same as your question, but Kevin’s replies to them may help with your issue:
It is the Longitude Latitude Height
For example, I am standing on a mountaintop, and I have the latitude and longitude of the mountaintop. I want to know the height of the mountaintop. It’s convenient for me to set the object to this mountaintop.