The problem is the sharp connection between the two filleted surfaces at the end of the flat, triangle-shaped surface. Try trimming the ends of all three at once with a single curve so that their shared edges create a curvature continuous edge, then fill with a G2 surface.
@Derek: not sure if you ever resolved this but if not, what I think engelhjs is trying to point out is his illustration is that it’s the singularity that’s causing the issue. If the surface is trimmed back so that there is no single point then it should be fine from there.