Cesium terrain altitude discrepancy


I am working on an application where I am interested in sampling the terrain altitude when a user clicks on the Cesium globe. What I’m finding is that there are large discrepancies in the reported altitudes between the Cesium terrain and Google Earth, which I am considering “truth” in this case. Is this to be expected, or is there something I am doing wrong/can do differently (use a different asset, missing an offset, AGL vs. MSL, etc.). I’ve included an example of the reported altitude difference that I am seeing.

Thanks in advance.