Consider the following scenario:
• You deploy Enterprise Voice in a Microsoft Lync Server 2013 environment.
• You call a Public Switched Telephone Network (PSTN) number.
• The PSTN callee puts the call on hold.
In this scenario, the call is dropped.
To fix this issue, install the July 2017 cumulative update 5.0.8308.992 for the Lync Server 2013, Mediation Server.