>>1880901in some models, some parts are separate material, and some of them are set to be transparent, to make them visible you will have to go to the material tab on pmxeditor and put 1 on "non-transp." on those invisible meshes
sometimes if there are too many materials, set to wireframe mode on pmxview so you can see if there's any hidden mesh once you undress the model
here's an example with a remilia model...which is also flat
welp here's the link
https://bowlroll.net/file/11619