In an installation of XenDesktop/XenApp 7.6 Enterprise, we see that on most of the clients the Taskbar Preview and the Windows Peek full screen preview of a minimized published application is not working correctly.

It seems that depending on the number of monitors connected, we either get no preview content at all, or in case we use 1 monitor we get a preview which contains vertical stripes.

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

Dynamic preview for multi monitors are disabled by default; this can be enabled by using below registry:
For 32 bit Operating System  
Registry Path : HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\ICA Client\Engine\Lockdown Profiles\All Regions\Lockdown\Virtual Channels\Seamless Windows
Name: EnablePreviewForMultiMonitor
Type: REG_SZ
Data: True

For 64 bit Operating System
Registry Path : HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Citrix\ICA Client\Engine\Lockdown Profiles\All Regions\Lockdown\Virtual Channels\Seamless Windows
Name: EnablePreviewForMultiMonitor
Type: REG_SZ
Data: True

OR

In the default.ica file for the Web Interface or StoreFront, in the [WFClient] section, add the entry "EnablePreviewForMultiMonitor=TRUE".

Problem Cause

Dynamic preview for multi monitors is disabled by default.

http://docs.citrix.com/en-us/receiver/windows/4-3/receiver-windows-43-about/receiver-for-windows-4-3-fixed-issues.html