The default behavior in Citrix Virtual Apps and Desktops, when launching applications, is to attempt to reuse existing sessions when possible. Application session sharing saves the costs of launching new sessions helping applications start faster and use fewer resources. It also offers other features that involve the clipboard such as copy-paste operations.

However, in some circumstances it might be desirable to have each application instance start in a separate session. For example, this might be particularly useful when starting multiple application sessions in full screen mode on separate monitors.

With the 7.13 and later release of Citrix Virtual Apps and Desktops, the Broker Service exposes a new setting at the Application Group level named SingleAppPerSession to allow that.

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Instructions

Step 1:  Create an Application group

Step 2: Disable session sharing

Logon to one of the Delivery Controller and open Powershell
Load Citrix Powershell snap-in by executing Add-PSSnapin Citrix*
Set application group property SessionSharingEnabled to false and SingleAppPerSession to true by executing 

Set-BrokerApplicationGroup -Name "<Application Group Name>" -SessionSharingEnabled $false -SingleAppPerSession $true



This setting apply to users trying to launch the same app with the same user account on multiple devices or different app from the same client device.
 

https://www.citrix.com/blogs/2017/02/27/xenapp-and-xendesktop-7-13-launching-an-application-in-multiple-sessions/