When installing DS as an explicit repository, the following objectClasses are defined within the repo.ds-explicit-managed-user.json for the managed/user type:
This also includes an attribute for country:
However, the 'c' attribute is not an attribute for any of these classes so country cannot be used despite being included in the schema. If you add the 'country' objectClass, then 'c' becomes a MUST despite being non-required in the managed schema.
A simple solution would be to modify the 60-repo-schema.ldif file to add 'c' to the 'fr-idm-managed-user-explicit' objectClass as a MAY: