Continuing the discussion from Solid Inspector Heisenbug:
@IanR To answer your other question in that thread; why it’s not possible to subdivide that shape: the two cubes in that model share an edge. That means there are more than two faces connected to that face - and SUbD cannot subdivide that.
Version 2 of SUbD - coming soon - will be able to handle it. It can subdivide meshes with internal faces and models like the one you posted. However, I’m not sure if it produce a desired result.
Also, not that face directions will affect the subdivided result in SUbD v2. So you want to ensure your faces are all facing in a uniform direction.