This means that a member ID in your upload file matched multiple constituent records in Luminate Online. The data sync won't update a record if there is more than one match, because it could update the incorrect record. The best way to resolve this is to first determine if the records are duplicates. If so, merge the records appropriately. If one record is inactive in the duplicate pair, they can't be merged. For this scenario, edit the inactive constituent's profile and append "_removed" to the current member ID so the sync will no longer match on it. If they aren't duplicates, change the member ID in Luminate Online for the record that has the incorrect member ID.