It sounds like you might be experiencing a bug with the Mobile Viewer.
When downloading the model into sketchup, everything works as expected.
Which leads me to believe that your components were viewable in the “Last Saved View” of your SketchUp model?
I ask because as you may already know, the Mobile Viewer app does not currently respect layer visibility, or hidden geometry on a scene by scene basis. In order for the components to be visible in the WebGL or Mobile Viewer, You’ll want to make sure that your components are visible in the “Last saved view” of your SketchUp model prior to uploading your model to 3D Warehouse.
If they are visible in the last saved view, and are still not showing up in the WebGL and/or Mobile Viewer app, please share the 3D Warehouse link, or attach the SKP file to this thread so we can investigate further.