Hi Psygorn, it looks like you've got some edge fragmentation in the surface before you shell:





the other thing that's kind of problematic with your shape here is with this edge being a trim curve on a plane:



If you make a blend off of that, these edges will not be smooth to each other even though the surfaces are smooth where they touch:



If that edge was a natural edge of the underlying surface then you would get both surface and edge smoothness there.

it would probably be best to make that one single longer surface instead.

- Michael