How to reproduce: Being non-logged in I go to secure area, for example, /admin, it has to redirect to login_path which in my case contains #(for example /index#login), but url generated is /index. That’s because an additional attribute “_firewall_context” has been introduced in symfony 3.3.3 (#22943).
During generation of login_path url (in Symfony\Component\Routing\Generator\UrlGenerator.php) my _fragment added after parameters (http://index?_firewall_context=security.firewall.map.context.main#login) and lost after _firewall_context param is removed