Hi, wonder why there is no connected line there?
profile is like this:
Hi Wilson -
But then you should also wonder why there are no such lines in these locations:
The answer is likely that there is no crease splitting in Grasshopper. When you create an object from tangent input curves, the result will be a single surface.
The fact that there is a connecting line in that one location shows there’s a tangency issue in that location.
But, since you didn’t post your *.gh file with all relevant referenced geometry internalized, that is just speculation…
Note that, for many downstream operations, it is better to have a polysurface rather than a single surface. You could consider to loft (or extrude) single segments and joining them after that operation.