Migrate users after farm migration

Recently, after a migration from SP2010 to SP2013, we encountered a ‘problem’ with users. Certain users were found twice in ‘persons and groups’ under site settings of several sites. The differences between the two were: 1. domain\username 2. i:0#.w|domain\username (AD synced) If u would search for a user (perhaps for giving permissions) you’d find only…