This issue occurs when you start a video in an online meeting. It occurs because the client that you use does not receive the necessary information for multi-view. Note A back-to-back user agent (B2BUA) is deployed by using Microsoft Unified Communications Managed API.
Resolution
To resolve this issue, install the July 2015 cumulative update 5.0.8308.920 for Microsoft Lync Server 2013 Conferencing Server.
