There is no visible reason for ‘aa_’ prefix inside permissions related database records until it may stay from the older data imported from the other database with such ‘aa_’ prefix.
These articles describe how WordPress stores it’s roles:
1) Single site;
WordPress multisite stores user permissions inside a single database table ‘wp_usermeta’ in assumption that database prefix is ‘wp_’.
So look what ID your user has and try to get all permissions records related to this user with query like:
SELECT * FROM wp_usermeta WHERE user_id=1 AND meta_key like '%capabilities';
and look if a record with ‘wp_capabilities’ meta_key value is there or it is not.
If it is not try to rename ‘aa_’ to ‘wp_’ and look if it will help.
As always, it’s a good habit to make a fresh backup before any manual data change.