After you apply KB3172184, Microsoft Lync 2013 (Skype for Business) always connects directly to Front End servers through DirectAccess IPsec tunnels instead of the previous external connections to Edge servers. This issue may affect call quality during conferences and connectivity.
To work around this issue, use one of the following methods:
Create a firewall rule to block outgoing IPv6 from client to Front End servers' IPv6 addresses.
Disable IPv6 on Front End servers.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.