Geometry.IntersectAll - Why does it not intersect with XY plane?

Long story short. I am working on this, but i have issues with the Geometry.IntersectAll node.
I am at a loss here.

When i ‘unplug’ Solid.ByUnion in the Graph and run it i don’t get the diagonal you see in the image.
As soon as i plug it back in to the Geometry.IntersectAll i get that diagonal.

Geometry Scaling.