I have been trying to import Altium PCB’s into Kicad recently, and not every 3d model imported perfectly. I’m planning to create a bunch of Altium files each containing a 3d shape made in a different way, and try to import each one. I’ll post those files here, and create bugs when a file failed to import.
This seems like a circle extruded by Altium to get the 3D-shape. Kicad currently doesn’t support the feature to extrude a 3D-model on its own. So I’m not surprised this 3D-model is not imported.