Problem in connecting users

Hello:

I have an installation of ejabberd on a Debian machine. Sometimes, when I connect from some clients (like pidgin or Pandion), the user initiating the connection connecting ends, though ejabberd node appears as connected. That is, at any given time I have properly connected users and users who have not completed the connection.

If I run the command connected_users_info ejabberd I can see that for users who have not completed the connection, the priority appear as undefined.

Besides, does not always happen with the same users or with the same customers. What can it be?

thanks