problem in loft between a circle and hexagon
You do not need guide curve if you solidly work with surfaces !
Before sweeping, creating a flat surface with the hexagon along the circle. This will give the opportunity to sweep tangeance with the circle.
Use boundary surface hexagonal before circle and put it normal to the surface
You can choose the circle profile and put it tangeant to the surface
Now you need to knit all surfaces and "try to make a volume" with them. See my SW 2015 file.