Vertices not behaving smoothly after Subdivide This model was made by extruding 2 Bezier curves. I tried joining them at the four vertices but the subsurface doesn't work.
This is the result. I've tried to delete and recreate the vertices several ways but I always get the same or similar result.
Face orientation (normals) was the problem. Once I rebuilt the parts from scratch and made sure to extrude both wireframe in the same direction the issue went away.