I added users but don't see them under the Users section of the Security tab. What's happening?

This is a known error with versions of Stardog prior to Stardog 8.2.0. You can solve the issue by upgrading to Stardog 8.2.0 or greater. 

You can also see your users in the CLI using the command stardog-admin user list (docs).

For more information on Studio, please see the docs.