1. Data conversion failed from Brep to Rectangle

Quite possibly yes, depending on how it’s done.

3. Attach minimal versions of all the relevant files

The Clipper plugin PolyOffset allows a smaller inner offset, as expected, but had a bizarre sequence problem that required using the first offset as the basis for the second offset.


Voronoi_2020Sep21b.gh (18.9 KB)

By the way, I just noticed that your random heights apply to only a very limited number of buildings in each group.