Loss of Something on conversion

We had a some issues on conversion. (see below images and descriptions)

**1. It seems that the surface of button is somehow partially gone.**
(The number of triangles is not changed, while the number of vertecies is decreased 1,088,424 to 264,382 on conversion)

obj-original

gltf

**2. It seems that the unnecessary plane has added.**
(the number of vertecies is decreased too)

obj-original

gltf

I don't know if these 2 problems are related to issue #235, #212 or #204. still occured in v3.1.0

**3. The RGB color applied on grey scale texture image is missing on conversion. See below the material definitions in .mtl and the texture image.

`newmtl PT_FABRIC_FRONT_1322893`
`Ka 0.230915 0.199538 0.173866`
`Kd 0.898039 0.776013 0.676173`
`Ks 0.025778 0.025778 0.025778`
`Ns 5.000000`
`illum 2`
`d 1.000000`
`map_Ka 2.3mm_3_Edit.png`
`map_Kd 2.3mm_3_Edit.png`

2.3mm_3_Edit.png

left obj-original / right gltf

If You need these obj files, I can email it to You! : ) Thanks!