I was migrating Lync at my office from 2010 to 2013, and after the first Front End server was added to the new 2013 Lync pool I ran into a precarious issue. The issue was that users could call into the IVR but never made it to a help desk technician. After troubleshooting, I narrowed the issue down specifically to response groups were behaving like the agents were not actually a member. An entire weekend of troubleshooting later and I found that the response groups were trying to contact older SIP addresses for the agents. Several months ago, I added an additional SIP domain <externaldomain.com> to the list, and changed over the SIP address of the users. The Response Groups seem to be referencing the old SIP address of the agents. I created distribution groups to represent the membership, and then changes the response groups to use the distribution instead of the custom list. This seemed to fix the issue, and the response groups were working again.
