Hello,
Browsing through data I downloaded, I encountered several KML (KMZ) files that did not show properly in Google Earth; I did not investigate thoroughly, but for example South Africa and Australia files don't show properly. Maybe this has something to do with the order of inner and/or outer boundaries (clockwise or counterclockwise)? If I understand correctly, in a KML file an inner or outer boundary is always counterclockwise (see description in KML reference of the Polygon geometry type at https://developers.google.com/kml/documentation/kmlreference#polygon), while in shapefiles an outer boundary is always clockwise and an inner boundary always counterclockwise (if I understand the Esri shapefile format description correctly when reading the section about the Polygon shape type).
Hope this helps.
Kind regards,
Thijs