Menu items with path set to <current> are not rendered for anonymous users.
Steps to reproduce:
1. Install vanila Drupal and log in as admin
2. Go to /admin/structure/menu/manage/main/add
3. Create a test menu link item. Important: Use route:<current> as link.
4. Save.
5. Check frontend as admin user. The link is visible.
6. Check frontend as anonymous user. The link is NOT visible.
Issue is resolved by granting 'Link to any page' or 'Access any content' permission to anonymous users which obviously is not something we want to do.