Hi AJ,

Sync uses the IDnumber field to match users in the CSV with users in the database. So the manually-added users will need an IDnumber that matches the IDnumber in the Sync CSV file. Otherwise Sync may attempt to add the username again, which will fail.

A user needs the totara/core:updateuseridnumber capability in the system context to edit idnumbers in user profiles so you may need to get an admin to fix the manually-created accounts.