To resolve this issue, install the following updates:
When Office Communicator Object Model API (OCOM) calls resolve a SIP address of a contact, Lync 2013 tries to query the presence status of the contact. In this situation, Lync 2013 receives a 480 error, and then loses the connection to the front-end server. After Lync 2013 reconnects to the server, it tries to resend the subscription to query the presence status every 30 minutes. When it resends the subscription, Lync 2013 creates a new connection that has an old or an empty Security Association (SA). That causes the server to close the connection, and Lync 2013 signs out again. Therefore, the disconnection and then reconnection occurs every 30 minutes.