1. A concise explanation of the problem you're experiencing.
Unable to load b3dm, display fine in Threejs gltf-viewer
The 2 errors are about "KHR_techniques_webgl" not supported by threejs gltf-viewer
Non-dracoed B3dm loads fine in Cesiumjs
2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.
if hasVertexColors is commented in Cesiumjs code, then Cesiumjs can dispay it, without color
3. Context. Why do you need to do this? We might know a better way to accomplish your goal.
4. The Cesium version you're using, your operating system and browser.
Cesium v1.58