Peter, sorry for the delayed reply here. Did you ever figure out your problem? If not, you can try this build http://cesium-dev.s3-website-us-east-1.amazonaws.com/cesium/3d-tiles/Cesium-1.34.0-3d-tiles22035.zip which is a full Cesium release made off of the 3d-tiles branch. If you’re still having the problem with that build, it may be a bug in the branch and not on your end.