I tried searching for an answer for this. Closest I got was here: https://github.com/geo-data/cesium-terrain-builder/issues/4
I tried these solutions but it doesn’t seem appropriate because it looks like the heightfields that are suffering are from the upsampling. It looks like an issue with the precision used when upsampling.
My source elevation data has 30m spacing, the heighfields made with cesium terrain builder came out at zoom level 14 ( 9 meter spacing). The uploaded images show heightfields at a higher resolution than this, so I am assuming its upsampled. Even looks upsampled too much. That’s a lot of vertices!