Symptoms
In a Microsoft Lync Server 2013 environment, you update the Skype for Business for iPhone client to 6.18.2 or a later version. When the iPhone goes to sleep mode, you may notice that you can't receive any instant message (IM) notifications or accept any incoming calls.
Cause
This issue occurs because the Skype for Business for iPhone client can't be waken up after the application goes into background in the iPhone.
Resolution
To fix this issue, install the January 2019 cumulative update 5.0.8308.1068 for Lync Server 2013, Web Components Server, and then configure push notifications.
