I do not know if someone has the same problem:
Now there are two users, if one is A, one is B.
B the already login Spark, while A later sign in Spark. But B and A reaction did not see in the A Spark online.
A firewall is a privileged opening of Spark.
Whether to keep the response time line have to do with it? If you set a shorter response time, the faster the display user login Spark. But I do not know where Openfire of this set.