like the title said, the faces become invisible, i have tried things from triangulating faces to recalculating outside normals, but one thing thats weird is that, when i try to import it as a MeshPart the missing faces becomes visible, unlike what happened when i try to import it with “Import 3D”
i dont know why it happened but i just checked the normals and the “ring” that had its faces missing were looking weird so i just deleted it, copied one of the rings below and placed it exactly in the same spot and it fixed it.