I used the basic facade rule file and the roofs start rule that come with the Redlands Example to turn the tops of buildings from just shapes to roofs, then I applied textures (jpgs taken from orthos). The roofs display fine in CE, but in the web viewer, not only do they not display, but sometimes it makes the roofs disappear. I've attached two images, one from CE and the other from the web viewer to show what I'm talking about.
The CityEngine WebViewer does not display the back sides of polygons to speed up the display, only the 'front' of the polygon is displayed. CityEngine does both sides by default.
In CityEngine's viewport settings, activate 'backface culling' for the same effect.
Is the data you export static models (imported files) or created entirely in CGA ? If in CGA, you can use the 'reverseNormals' operation on those specific faces. If it's imported data, then you'll have to manually clean the data or ask the data provider to fix the normals.
Does this all also explain the lost textures, or is that a second issue ?
Let me know..