I think I hit an odd bug while trying to split a curve. I am trying to split the red isocurve with the two blue curves. The blue curves were OffsetCrvOnSrf from the tan curves which came from the Intersections between the two green surfaces.
When I try in Rhino 7, I get the “Curves do not intersect or many not be in tolerance of each other” error. I tried to Pull all three curves onto the same surface and they still will not split or trim.
Copy and Paste into Rhino 6.19 and it all works just fine.
Split isocurve bug.3dm (1.3 MB)