Symptoms
Assume that a disclaimer or warning message is added to the beginning of every instant messaging (IM) conversation in Microsoft Skype for Business Server 2015. When you open the conversation window in Microsoft Skype for Business 2016, the client freezes.
For more information about how to add disclaimers or warning messages, see Adding custom text to instant messages in Lync Server 2013.
Resolution
To fix this issue, install the December 5, 2017, update (KB4011563) for Skype for Business 2016.
