If the users are signing in to an on-premises Lync Server 2013 deployment, you must apply Cumulative Update 1 for Lync Server 2013, and mobility must be enabled. For more information, go to the following Microsoft Knowledge Base article:
Updates for Lync Server 2013
If the users are signing in to Skype for Business Online in Office 365, they may have to wait until your organization receives the latest Skype for Business Online service upgrades.
For more information, see the following Microsoft websites: