Edge Split modifier not working on export

[Kaya47]

I`m having this model on which i applied an edge split modifier. When i export it as a nif file, there are portions where the modifier doesn`t work. Not only that but there are parts where the surface gets even darker. I didn`t have this problem until now, if i try to export something else it works fine. This means that it`s not the exporting script that`s having problems, it`s the model itself.

And the normals are not flipped, i even tried a Ctrl + N and got the same thing.