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i think citrix policy overrides GPO for idle/disconnect policies on newer version of citrix now, check both the Microsoft GPOs and the Studio Policies for any conflicts

i´m not talking about ICA disconnects. The connect from the Application running on the RDSH to its Application Backend Server (a SQL for example) is terminated after inactivity.

Several "homemade" applications require the following registry key on newer operating systems:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\TcpIp\Parameters

KeepAliveTime

DWORD=600000

Thanks for that @Balint Oberrauch, problems are gone. However i first didnt get, that these keys have to be set on the application severs (which werent modified at all), not on my RDSHs.