Consider the following scenario:
You deploy two paired Front-End pools in a Microsoft Skype for Business Server 2015 environment.
You perform a pool failover to fail over to the backup pool.
A user creates a Skype meeting.
You perform a pool failover to fail back to the primary pool.
You join the meeting that's created by the user.
In this scenario, you can’t join the Skype meeting.
This issue occurs because the conference data is inconsistent between the primary pool and the backup pool.
To fix this issue, install the following updates: