Symptoms
Consider the following scenario:
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You are homed on a Survivable Branch Appliance or Server (SBAs) in Microsoft Skype for Business Server 2015.
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The advanced privacy mode is enabled in SBAs.
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You use a UCWA client such as the Skype for Business for Mac or mobile client.
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A federated Skype for Business user starts a call to you.
In this scenario, you can accept the incoming call. However, the call is a one-way audio from the UCWA client to the federated user, and no audio comes back. After about 15 seconds, the call drops. In addition, the outgoing call isn't affected.
Resolution
To fix this issue, install the May 2019 cumulative update 6.0.9319.548 for Skype for Business Server 2015, Front End Server and Edge Server.
Workaround
You can start an outgoing call to the federated user or let this user invite you into a meeting.
