We have had this error a few times. You just need to open those three users in the Canvas UI and fix the incorrect information for each user. The user file won't fix things like that. Just verify that each user has the correct name, login ID, and SIS ID in the Canvas UI.
You'll want to correct the error in the SIS database or wherever your user file was built from first though. In my experience, the error on the SIS side is usually fixed by time I go looking for it so you might just need to verify it's correct there before making changes in the Canvas UI. You would be checking to see if any of the IDs are duplicated.
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