i had the same issue
it is nothing to do with the user name
i have mine set to other thing than “admin”
..here is what i did & now i’m the Super Admin ^^
Just swap the multisite lines in the wp-config.php
to be in that order
define( ‘MULTISITE’, true );
define(‘WP_ALLOW_MULTISITE’, true);
Hope it works with you too ??
