Symptoms
This issue occurs after you apply the November 10, 2015 security update for Microsoft Lync 2013 (Microsoft Skype for Business). When this issue occurs, you can't receive any missed call notifications if your account isn't enabled for Microsoft Exchange Unified Messaging (UM).
Resolution
To fix this issue, install the February 9, 2016 update (KB3114732) for Lync 2013 (Skype for Business). Note Lync 2013 was upgraded to Skype for Business in April 2015.