avtr_bae1393b-33dc-4cbf-9667-9bc1ccfad172 (my personal main avatar, using the most recent version of Mochies Uber Shader)
If you use stencil outlines with a shader that supports them, then anything that material touches will show as all black (presumably the outline color, ive just only seen black)
Stencil outlines also break the preview of the model if you click on it in the assets folder, its what clued me into finding out what was likely breaking it.
So far ive seen atleast one other person with the same issue, and i confirmed with them that they were also using stencil outlines with their model.