BuddyPress.org

I just tested it and it works properly. [ Don’t use an ‘exit’. ]

function test() {
    echo "<br>test worked!<br>";
}
add_action('bp_after_registration_confirmed', 'test');

Are you using a custom register page?
If so, does it have the do_action hook you’re trying to use?

Also try it with a standard WP theme like 2015.