Super Text Mesh uses submeshes to render, so it's possible the mesh data will be inside of that data block.
https://docs.unity3d.com/ScriptReference/Mesh.GetSubMesh.html
This should be what you need to get a single mesh out of a mesh that uses submeshes. STM will make a new submesh every time the material changes.
Then, see what texture is on the corresponding mesh with STM's meshrenderer, and getting the material at the same index as the submesh. Hooopefully this works, and it was just the submeshes causing the issue.