When you start an ad hoc audio conference in Microsoft Skype for Business using Citrix RealTime Optimization Pack 2.0, the remote participant tile displays a blank tile instead of the dominant speaker in the conference window.
Note This issue doesn't occur if you are invited to the ad hoc audio conference.
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. And Citrix RealTime Optimization Pack 2.0 requires the Skype for Business client.