How to get rid of sharp edges when using subsurf modifier? I am currently playing around with the Catmull-Clark part of the subdivision modifier and I'm starting to get the hang of it. However, I have one edge that does just weird things:



I want to have a smooth rounding here, but somehow the edges and vertices of this region don't seem to cooperate (other parts of the same mesh are fine).

I tried rebuilding this section from scratch and checked for hidden/inside faces or edges (didn't find anything). I joined adjacent vertices and am pretty sure there are no double vertices, edges, anything. There is a mirror modifier in front of it, but it doesn't interact with this particular region. I'm currently out of ideas and welcome input.

File (Has been cut down to the tricky part.):

http://www.mediafire.com/file/8u5tqhf1wyonr0y/for_stackexchange.blend
As we see if we enable the Face Orientation option in the Viewport Overlays, you have some flipped normals, Blender can't smooth correctly between the faces. In Edit mode select all and press ShiftN