Works for me - bridge@EWC, V10.21.02, AP3705i, in my case I've blocked traffic as that was easier to test.
Note: it took some minutes before the traffic was blocked so I'm not sure whether I've done something wrong or whether there is some sync happening until it's active.
Have you enabled application visibility on the WLAN service ?
Back to the overall goal...I'm not sure whether I unterstand the setup..
the WLAN service is set to authentication for external captive portal and the screenshot show the unauthenticated traffic role ?
And then in case someone uses facebook, mail it should redirect to the portal and the user needs to authenticate on the portal ?