This sphere is made of 108 parts. Some of them are parts, some are unions authored in studio, and some are unions generated at runtime. None of them will union with any other part in the model. It looks like they’re all giving code -6.
CSG operations between PartOperations created at runtime and PartOperations created within Studio are not currently supported. We might enable this in the future but do not have any timeline to share at this point.