After launching a published desktop, the screen turns black following the Windows Welcome screen.
After waiting for a specific amount of time, the desktop loads successfully.
This behavior occurs every time a user starts a new session on non-persistent VDI machines.
The duration of the black screen is consistent for each user and session.
The "Run logon scripts synchronously" Group Policy is not being used.

Caution! Refer to the Disclaimer at the end of this article before using the Registry Editor.

Disclaimer:

"Caution! Using Registry Editor incorrectly can cause serious problems that might require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it."

By default, when Winlogon attempts to launch Explorer, logonui.exe will exit after a 30-second timeout. During this period, the screen displays “Please wait.” If Explorer cannot show desktop within 30 seconds, logonui.exe exits, leaving no process to render the desktop - resulting in a black screen.

On the affected machines, the DelayedDesktopSwitchTimeout value is set to 1 second. This causes the black screen to appear almost immediately after Explorer starts. As a result, users briefly see a black screen until Explorer finishes loading. However, this behavior does not indicate a functional issue.

Remove the following registry value on the VDA machine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
REG_DWORD: DelayedDesktopSwitchTimeout
Value: 1

For MCS or PVS provisioned machines:
Delete the above mentioned registry value.
Update the machine catalog to make the change apply to all provisioned machines.

When launching a published desktop, users may see a black screen immediately after the Windows Welcome screen. After a short, fixed delay, the desktop, taskbar, and Start menu appear normally.