Citrix Studio shows the message Mandatory Upgrade

• Make sure to take backup/snapshot of all Delivery Controllers.
• Backup Site, Monitoring and Logging databases.
• In a maintenance window reboot all Delivery Controllers.
• Close all Citrix Studio sessions from Delivery Controllers or any management server.
• Access only 1 Delivery Controller server through RDP connection, open Citrix Studio, and click on "Start the automatic Site upgrade".
• Wait till complete upgrade. Mandatory upgrade message should not appear anymore. 

If above steps does not resolve the issue please check if all Citrix services are configured with right database. If required update it.

You can validate it executing following PowerShell commands on each Delivery Controller.

Add-PSSnapin Citrix*

Get-AcctDBConnection
Get-AdminDBConnection
Get-AnalyticsDBConnection
Get-AppLibDBConnection
Get-BrokerDBConnection
Get-ConfigDBConnection
Get-EnvTestDBConnection
Get-HypDBConnection
Get-LogDBConnection
Get-MonitorDBConnection
Get-OrchDBConnection
Get-ProvDBConnection
Get-SfDBConnection
Get-TrustDBConnection

Problem Cause

N/A