Microstation Models not displayed in cesium

1. A concise explanation of the problem you're experiencing.
I am trying to show some models in cesium for a particular project. In this project we are creating models in Microstation. These are then exported to collada, which i than convert to glb/gltf to show on cesium. but it fails to show in cesium. We have tried every possible alternative viz. from microstation to SketchUP or Microstation to ArcScene etc. The Individual models itself are very light weight (e.g. single house without texture)
when we export from microstation to SketchUP and than to gltf i get a success of 5% means of 100 models converted only 5 can be shown in cesium. All the Models work pretty much fine in rest of the softwares which reads 3d models.

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.
var urlModel2='./ColladaModels/sample/building_su.glb';
  var entity2 = viewer.entities.add({
    name : urlModel2,
    position : Cesium.Cartesian3.fromDegrees(-3.238563,51.639650,0.0),
    model : {
        uri : urlModel2,
        scale: 0.85

The above model is exported from Microstation to SketchUP to GLB which gets displayed in cesium.
There is no bug or error shown when loading the problematic models.

I would like to submit some problematic models so that someone can take a look and let me know whats wrong in them w.r.t. Cesium....

i have uploaded and shared some problematic models to my google drive as i couldn't find an upload method here.

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.
We want to model a city in 3D, for this we are using Microstation to create the Models as it's more fast for production work.

since our models are small size we are using the online convertor...

4. The Cesium version you're using, your operating system and browser.
v1.39 Windows 7 and Chrome Version 61.0.3163.100.

Looking at the .dae files the transparency is 0.0. Once these values are set to 1.0 instead the models show up in Cesium.