I have several models that share the same material, but they each have the same material assigned as a child object. I wanted to be smart and copy the unique materials to a "Materials" folder and just use them from there (to only have them once).
However, this broke the visuals of my models. It's suddenly as if the UV changed.
I guess I have two questions now:

1. Why does this happen?
2. I can't undo this problem.... How do I fix this? I can't easily get the source assets.

Could you add some images to describe the problem?
UV's won't change unless you use mesh \ extract from atlas, or convert to atlas, or manually change UV's for meshes in the mesh editor.