I found Brep.Split has no problem.
I missed when split returns nothing(empty array).
I hope another friends do not misstake such as I did. ^.^
spliterror.3dm (489.2 KB)
I’m in trouble with splitting brep.
I found BREP split result sometimes some missing part of it.
I uploaded the file and image.
I made splitter as below, x,y,z directon(1/2 of boundingbox)