Symptoms
Assume that a Microsoft Microsoft 365 Apps for enterprise user has set delegates and call forwarding. When the user signs in to the Microsoft Skype for Business Basic client, the delegates and call forwarding settings are removed and turned off.
Resolution
To fix this issue, install the December 5, 2017, update (KB4011284) for Skype for Business 2015 (Lync 2013).
Note Lync 2013 was upgraded to Skype for Business in April 2015.