@lelinhphuong & gwtmh: there are no known problems with the blue arrow nor has anything changed on our end; all issues reported have been related to javascript not working on the user's end. Please check the FAQ here: viewtopic.php?f=1&t=1424249 and PM me if you still can't get the blue arrows to show.
Same issue here. Javascript enabled. I don't see the blue arrows at the moment.
ETA - as another user reported, if I hit the thank you button, the blue arrow appears.