ICA session gets disconnected when the web session times out.
To resolve this issue, set logoffAction to None to leave users' applications running when they log off from the site or when the web session times out.
Steps to set the logoffAction to none on Storefront Web.config
1) On your Storefront server navigate to C:\inetpub\wwwroot\Citrix\"StoreName"
2) Edit the Web.config file using notepad.
3) In the web.config file go to the Logoffaction and change it to none.
logoffAction="none" showReconnectButton="false" showDisconnectButton="false" />