Symptoms
When you try to rename a contact group and use the Delete key to delete some characters in Microsoft Skype for Business 2015 (Lync 2013), the contact group is deleted unexpectedly.
Resolution
To fix this issue, install the November 7, 2017, update (KB4011255) for Skype for Business 2015 (Lync 2013).
Note Lync 2013 was upgraded to Skype for Business in April 2015.