OK I took a look at both of the meshes (Karina's and Movida's). Neither of them had the vertices welded at the center of the cap.

So I started with Karina's mesh, and deleted the half that looks like she mirrored (the materials were appended with the number 2, so I figured that was the duplicated one.)

Then I did some geometry tweaks ... in particular there was a polygon or two missing in the hat band, and there were some unnecessary edges in the back of the hat that seemed to be doing funky things, so I removed those.

After that, I selected all of the center vertices and made sure they were at 0-coordinate (making them perfectly centered).

Then I mirrored the geometry inside Modo, and then did a Mesh Cleanup. After that I turned subdivision on, and noticed that it was subdividing kind of funny near that big circle on the top. I selected what LOOKED to be that one vertex. BUT ... Modo reported that I had 16 vertices selected. So, I joined all 16 of them into a single vertex. Hopefully now you won't get a hole in the top like before.

I HOPE I found all the errors. Yeah, that mesh was def FUBAR. If it still isn't working let me know. I emailed it back to Movida.