Having the same issue.  
As far as I can tell, it seems to happen for me when there are nested recursions?
For example:  a depends on b, b depends on c
`guix import  pypi -r package-c` - works
`guix import  pypi -r package-b` - works, importing both b and c
`guix import  pypi -r package-a` - downloads a and b, but fails at c.