On a XenApp 7.x, published App or Desktop, launches but immediately disconnects. The session disappears from client machine and it shows disconnected on VDA and in Citrix Studio.
The application instance is still running on VDA.

Remove any additional entry apart from "C:\Windows\system32\userinit.exe,"  at following registry path

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Userinit

Problem Cause

Ideally the Winlogon.exe reads “HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\” and uses userinit.exe to launch cmstart.exe and wfshell.exe. However, in the affected environment, you may see additional executable path  specified apart from userinit.exe which attempts to launch a duplicate instance cmstart.exe and wfshell.exe and causes the issue