Okay sorry dude I missed some part it seems.

Well, the final solution to your problem is that you still got non manifold edges >> means some face-normals are outwards your model, and some are inwards. Creating a disturbing polys topology that can't be transformed in SubD.

Polygon >> Cleanup : activate only "Nonmanifold geometry" checkbox . Cleanup Button.

Then, you're back to SubD

ps : I don't know your level, so sorry if I write down too much details you already know, it's another habit willing to tell all without dropping the details.


Cheers