Just by adding a user as and Administrator in Jira doesn't automatically give the person access to everything. It all depends on the Permission Scheme attached to the Project. Make sure the person has at least Browse Project to see the project.
As John said, Admin rights gives you admin. Not "can see everything".
Please check the browse project permission for the projects you want this person to see (as they're an admin, they can do that themselves, but you should explain to them that admin = admin, not "bypass all the permissions")
Members of the Administrator group do not have permission to manage users.
A user needs to be a member of site-admins to manage users for the site.
For JSM June Challenge #2, share how your non-technical teams like HR, legal, marketing, finance, and beyond started using Jira Service Management! Tell us: Did they ask to start using it or...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events