I couldn't split the Brep anymore

Hello everyone, as you can see, I want to use the horizontal surface to cut the vertical surface. But there is a big problem with the split surface, I don’t know what my problem is, is there any way to fix it? Thank you all in advance! :sob:

problem.3dm (82.1 KB)
problem.gh (14.8 KB)

I tried to edit the curve again, and it was solved, but seems weird, cause of the curvature. and another question, does anyone know how to cut polysurfaces with curves? I have tried split surface and some other methods, but it doesn’t work…: (

problem 2.3dm (91.9 KB)
problem 2.gh (22.5 KB)