I am having issues with PlanarSrf and selfintersecting curves.
Hatch also has issues with this, as the result becomes an “invalid geometry”, but if I then explode the Hatch I get the surface I want.
Hatch with your example curve created a bad object over here. I´ve been using TestGetPlanarRegions with CombineRegions=No for cases like that so i can later delete what is not required.
This is always the problem with “non-manifold” joints (more than two curves or surfaces at a junction). Hard to figure out what’s inside and what’s outside…