Region Slits (rslits) - Unpredictable results - msg: "Shape Must be a Planar Region"

Here I have been trying set up GH so that I can stack and union solids in Rhino and have a live output of surfaces with lasercut-ready notches for a waffle model. The region slits component is supposed to do this, and in some cases it does.

I know that people use GH to make waffles all the time, but I can not get this component to produce satisfactory results. I want to: produce slits in two sets of surfaces derived from X and Y contours of a closed, solid polysurface in Rhino.

Can someone help me understand why I am not getting correct results? I rebuilt my original vault to make sure that I have a good surface. No naked edges, no non-manifold edges. I could come up with a lengthy workaround for this, but I want to know how to make the component work, or how people usually go about this.

See the attached grasshopper and rhino documents for information. Note the (baked) output of the rslits with the closed, planar curves yields some satisfactory regions with slits, but it excludes many input surfaces.

Thanks in advance!! (12.9 KB)
Vault-Builder-v2-help 001.3dm (1.6 MB)