All of my materials showed up as missing texture, and I saw /t/6404592/need-some-help where the original poster later has my same issue, and they said:
In Blender before exporting I tried setting the material to just a flat colored one, and after exporting it and readding my texture in the editor it wokred for some reason?
So after that I tried making a new material, which suddenly worked even though my original ones in Blender were mostly already flat-colored materials, and then it worked for the new one! So then I realized why: all my materials had been named like Material.001, Material.002 and so on (default blender naming), but the new material was just named "Material" by Blender, which didn't have that problem.
So then I renamed all my materials and the problem went away!! yippee
so,, probably the troubleshooting should mention this, or maybe the software could be updated to automatically rename the materials? I assume other chars might have the same issue
Amazing work on this btw,,, it works really well!!