I have a pretty basic cityGML file that contains a couple hundred cylindrical volumes but when I inspect the converted tileset result it looks like this. I did not turn on clamp to terrain and all the cityGML objects are of type GenericCityObject which isn’t a supported clamped type. I have a bunch of cityGML that gets generated through the same process and it seems I only get this behavior with circular geometries if that helps any.
And here is a video showing similar issues on another circular dataset
You can download the source data here to test out