Jira Core and Jira Software
Users will appear in any user picker and in mention (@) even if they don’t have application access at that time but only if they don’t have “Jira Administrators” or “Jira System Administrators” permission!
Users with “Jira Administrators” or “Jira System Administrators” permission
Users who have “Jira Administrators” or “Jira System Administrators” permission won’t appear in the user picker and in mentions while the License Optimizer is active and the user doesn’t have access at that particular time.
Workarounds
Check who has “Jira Administrators” or “Jira System Administrators” permission and make sure all of them actually should have this permission.
Add Users or Groups with “Jira Administrators” or “Jira System Administrators” permission to the application access menu.
Create a separate account for users that should have “Jira Administrators” or “Jira System Administrators” permission and add these accounts to the permission. The users will be able to switch account if any of their action requires administrator permission.
Create one “Jira Administrators” user and grant access to employees who needs it.
Jira Service Management
Users with active application access will be visible in the Service Management user pickers!