OffsetFail.3dm (359.8 KB)
The offset srf has a strange kink.
To retrace, try with the original curves.
RailRevolve the black curve along the green star-like curve.
OffsetSrf 0.8 to the inside, loose=yes.
See the kink at the srf seam.
V5 does it well, no kink.
It goes even worse:
CrvSeam the green curve to a quad point.
See the change of the control points at the original position.
And the new distribution at the new seam point.
Try the above with the altered green curve.
This fails in V5 then as well.