In creating construction planes as surfaces in Grasshopper/Python/Rhinocommon I have had to stop creating them in a way that they both intersect at their origin or I can no longer reliably get an intersection between them to come out of Rhino.Geometry,Intersect.Intersection.BrepBrep(…). When creating them I just kludge factor one of the size domains to 1.1X in the negative range. This is a general Rhino error however, since I can bake to Rhino from Grasshopper and reproduce it. Any movement or surface edge editing restores the line intersection being found properly. I’ve reparameterized the domains in Rhinocommon, to no effect. The same thing happened when the large surface was left as a plane to use BrepPlane intersection which is why I switched to BrepBrep.
Rhino Intersection Bug Report V2.3dm (58.4 KB)