When this issue occurs, the Lync Server Response Group service on a Microsoft Lync Server 2013 front-end server is stuck in the Starting state. Additionally, the https://web_pool FQDN /RgsClients/Tab.aspx page times out if you click the Response Group Settings option on the Tools menu in a Microsoft Skype for Business client.
This issue occurs because the topology snapshot was recomputed multiple times by the Response Group Service.
To resolve this issue, install the September 2015 cumulative update 5.0.8308.933 for the Lync Server 2013 Response Group service.
Note This update redesigns and optimizes the computation of the topology snapshot.