Two IP Office users can only see each other's presence status and exchange instant messages if they are members of the same XMPP group in the IP Office system configuration. Each user can be a member of one or more XMPP groups.
If a new IP Office user is added as a single action (add user, add new user to XMPP group, save configuration), the user is not seen in the portal view of the XMPP group. The resolution is to then make some further XMPP group configuration change or to restart the portal service.
To avoid this, you should save the configuration between each action (add user, save configuration, add new user to XMPP group, save configuration).