Help! Why is my avatars eyes/mouth clipping through face?

I am trying to edit my model in blender, and I am running into trouble with materials. This clipping problem also occurs when I import my model into Unity and then VRChat.

This is what my model looks like without material preview on. This is how I want it to look.

This is what it looks like with material preview. You can see that the face skin becomes transparent so you can see the mouth and eyes through the skin. This is wrong.

This is what the face mesh looks like, if that matters.

Any advice would be appreciated. I got this model from DeviantArt, so I don’t know how to edit in Blender that well yet. Is there any way I can fix this?

Are all the faces facing the right direction? Try checking them from the Viewport Overlay > Face Orientation.

Does this avatar use a shape key? If so, try making sure you are not working on any other key that’s not “Basis”.