I think there are some problems with exporting a single plain Cube from MoI.
In Carrara, for it, using Vertex shading domains seems the quickest..
Quite odd! (Will study some more)

However, I am reading that Modo is only importing anything as a solid---- not in parts--from MoI?
In Carrara, all the file type imports seem to arrive in parts. Especially the LWO file type which Modo should accept ok.

With OBJ file, this little dropdown in Carrara has to be selected as shown to get the parts separated. I would be surprised if Modo did not have similar.

Note. I just don't use UVs.

Brian