Grasshopper : Issue in generating 3D surface after lofting and Brep cut

I am having issue in generating a 3D surface after cutting.
After cutting there is projections/warping of surface.

Before cutting

After cutting with plane

Hi - that looks like a coarse display mesh. You can change how these are generated. For Rhino, see
In Grasshopper, you have these controls:

If that doesn’t do it, you’ll have to post your Grasshopper definition.