Symptoms:
- Sessions seems slow, unresponsive. User input does not seem to be processed. This applies to seamless applications and desktops.
- It seems like ICA screen updates are not received, although bytes are received when you check network traffic information in the Connection Manager.
- After pressing Shift+F2 (toggle seamless mode) you will suddenly notice the screen updates that resulted from your input.
The Citrix Web Interface is enumerating applications normally. ICA sessions to the terminal server are succesfully established. This ruled out authentication, XML and STA related issues.
Cause:
Turns out this was simply an ICA client related problem. Citrix Receiver 3.4 seems incompatible with the Citrix MetaFrame Presentation Server 4.0 legacy farm. At least when using session reliability.
Update: the issue persists in Citrix Receiver 4.0.
Solution:
Use Citrix Receiver 3.3 or earlier.
... or (thanks to this post), you can set DeferredUpdateMode to False by editing your Windows registry.
On 32-bit systems
HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\ICA Client\Engine\Lockdown Profiles\All Regions\Lockdown\Virtual Channels\Seamless Windows\
Download and import .reg key
On 64-bit systems
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Citrix\ICA Client\Engine\Lockdown Profiles\All Regions\Lockdown\Virtual Channels\Seamless Windows\
Download and import .reg key
A reboot is not required.