Limitations of Bulk loader in Relationship Attribute Level

Bulk loader cannot update the task operations on the user objects in the relationship attribute level.

Relationship attributes that are not updated by Bulk Loader are Users Access roles, Users admin roles, Users Provisioning Roles, Users group membership, and Groups group.
Relationship attributes that would get overwritten when you replace old attribute values with new attribute values from the bulk loader file are Groups Administrators, and Custom or default Multi-valued attribute.