Summary
This issue occurs because the conference signatures are not deleted from the routing group's metadata when Windows fabric is closing a routing group replica on one Front-End server. To fix this issue, install the July 2018 cumulative update 5.0.8308.1001 for Lync Server 2013, Front End Server and Edge Server and the July 2018 cumulative update 5.0.8308.1001 for Lync Server 2013, Core Components.
