Symptoms
In Microsoft Skype for Business Server 2015, when a Skype for Business on Mac client user tries to add a new participant to a peer-to-peer call that has a screen sharing by using the Video-based Screen Sharing (VbSS) feature, you may find the escalation fails and the participant can't receive the meeting invitation to join the peer-to-peer session.
Resolution
To fix this issue, install the January 2019 cumulative update 6.0.9319.537 for Skype for Business Server 2015 and Unified Communications Managed API 5.0 Runtime.
Workaround
To work around this issue, refer to the following article to disable the VbSS feature in Skype for Business Server 2015.
