Summary
In Microsoft Lync Server 2013, a user may intermittently can't do some actions such as joining an instant message (IM), joining a meeting, or calling another user that's homed in a different pool. This issue occurs because the user's affected Front-End pool is running a very old Intercluster routing component. To get the update for the Intercluster routing component, please install the January 2019 cumulative update 5.0.8308.1068 for Lync Server 2013, Front End Server and Edge Server.
More Information
For more information about the Intercluster routing component, go to the following website:
General information about the Intercluster routing component
