Improvise, adapt, overcome 
There are aspects of your code that can cause problems, such as tween (eliminated) and offset curves. This morning I tried Sweep 2 using arcs instead of Loft, but that results in a polysurface instead of a single surface so fails downstream. You might be able to work around that?
Then I tried NetSurf (Network Surface) which seems to work but can be excessively slow. Area in particular can take more than four minutes!! Custom preview can take most of a full minute!!
And there are issues about the resulting surface shape, depending on the number of V curves (arcs) and the “offset” of the bulge (150, 250 or more). I’ve spent a lot of time on this and am done for now.
I rearranged some code (the data dam) so you can see many of the results immediately. Be prepared for a long delay when you activate the data dam though, or open the file the first time.
area_calcs_2023Dec26a.gh (23.5 KB)