When you receive a message that contains many emoticons in Microsoft Skype for Business 2015 (Lync 2013), the client freezes and requires a restart to recover.
To fix this issue, install the October 2, 2018, update (KB4461446)for Skype for Business 2015 (Lync 2013).
Note Lync 2013 was upgraded to Skype for Business in April 2015.
After you install this update, if more than ten emoticons are sent within a message block all emoticons within the block will be converted into text. For more information, see Emoticons and emojis converted to text if more than 10 are sent in one message block in Skype for Business 2015 or 2016 clients.