Here’s what happens with your mesh when FitLoft replaces Loft:
Clearly the FitLoft object uses a much different method for defining the loft surface. There are differences between between the 2, but they don’t seem to be too large. I can’t explain any of this of course, but it is interesting and will hopefully help you some.
Arm-voronoi-bb3.gh (43.8 KB)
Note that I changed the cylinder shape to an elliptical one just to make the thumb hole a little nicer. Also, playing with the Voronoi Seed parameter changes the structure where the hole needs to be.