If a nation is on the Organization plan and has renamed one of the standard permission sets they are unable to move to the Leader plan. In order to change plans you need to have the Admin and Staffer permissions only.
Update 10/31 - this is complete! When you go to settings > Permission sets > Active > edit the name field is now an editable text box - so you will be able to switch plans.
This is a fix that could be helped by allowing users to change the name of a permission set. We hope to have more information on this soon and will keep you posted.