Symptoms
Administrators who are members of the RTCUniversalServerAdmins group in Microsoft Skype for Business Server 2015 but not members of the Sysadmin fixed server role in SQL Server role can't run the Invoke-CsPoolFailover and Invoke-CsPoolFailback cmdlets. In addition, they may receive a "SELECT rights to dbo.Item is not present" error message.
Resolution
To fix this issue, install the July 2018 cumulative update 6.0.9319.534 for Skype for Business Server 2015, Core Components.