I think you are running into Mendix built in security that is based on User Roles. In the Project module (the top one in the Modeler), open the Security object. Click on User Roles tab and open one of your roles (Administrator, for instance). In the popup window, you'll see which user roles can be managed by the user role you opened. For instance, Administrator user role is usually set up to manage users with all roles. If you login with a user role that cannot manage all user roles, there are a number of attributes you won't be able to view for users you can't manage (active, blocked, etc.). This article gives a bit of information about Project Security: https://docs.mendix.com/refguide/project-security
Having said all of that, are you able to view FullName if you login with a user that has Administrator user role? (I am assuming that Administrator is set to manage all users). If you can view FullName as an Administrator, then the issue you are experiencing is related to Project Security and you'll need to spend some time on your project security structure to accomplish what you want to.
Hope that helps,
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