The following screenshot depicts bad mesh. It is made of a mesh and a triangle. I cannot select the mesh, but I can select the triangle. It takes about 4 seconds to move this mesh with the gumball. I made the mesh by extracting it from bigger mesh with ExtractMeshPart command.
When I use RebuildMesh command, the triangle disappears, but it reappears when I move the mesh with the gumball.
bad mesh.3dm (110.9 KB)