Known issues in HDX RealTime Optimization Pack
Known issues in 2.9 LTSR CU4
No new known issues have been observed in Cumulative Update 4.
Known issues in 2.9 LTSR CU3
When using macOS Big Sur version 11.2, the About option in the HDX RealTime Optimization Pack might display the OS version as 10.16.0. [LOP-4466]
In a multi-monitor environment, when using Skype for Business in seamless mode to receive a video call, the video overlay might be displaced from the Skype for Business window. The issue occurs with the macOS running Big Sur. [LOP-4475]
Known issues in 2.9 LTSR CU2
No new known issues have been observed in Cumulative Update 2.
Known issues in 2.9 LTSR CU1
No new known issues have been observed in Cumulative Update 1.
Known issues in 2.9 LTSR
Editing the registry 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.
General known issues
If macOS X user changes the dock UI setting while Skype for Business is running, current and future calls don’t display local or remote video. [LOP-1062]
Workaround: Restart Skype for Business.
When fallback mode is set to audio only, and the users in fallback mode participate in a video conference, they might see their own states in the participant list incorrectly displayed as On Hold. Other users are not affected. [LOP-1175]
If a caller plugs in another human interface device (HID) during an active call, the call might drop. [LOP-1377]
After the called party using an IP phone accepts a video call as audio-only, the caller cannot add a third participant to turn the call into a conference call.
Workaround: The called party can add the third participant, after which all conferencing capabilities are available. [LOP-1504]
The Optimization Pack is not compatible with the Polycom RealPresence Trio 8800. If you use the Skype for Business UI to accept a call, but use the Polycom RealPresence Trio 88 to hang up the call, the call doesn’t end. [LOP-1983]
Video capture issues sometimes occur when using a Logitech 9000 camera and the Citrix Ready workspace hub. The Preview option might not work, call initialization might be slow, calls placed on hold might not resume, or the camera fails during a call [LOP-2339]
When starting an audio point-to-point call and starting video at the same time, a Cannot start video message appears. [LOP-2356]
Workaround: Do not start an audio point-to-point call and video at the same time.
In point-to-point calls using a UVC camera, or in a Meet Now, before a user starts transmitting video, the aspect ratio of the picture-in-picture video window might not display in the correct aspect ratio. On point-to-point calls, the video you’re sending might be wider and include more content than what is visible in the picture-in-picture window. In Meet Now, after each participant becomes an active speaker, the aspect ratio changes to 16:9. [LOP-2462]
When a call is started on a Chrome OS device using a webcam microphone and a Polycom CX100 speaker or a built-in speakerphone/microphone, echo cancellation might not work. The remote participant in the call might hear their own voice at a low volume. Background sounds from the originator can also be heard. [LOP-3082]
While changing resolution in a peer-to-peer or conference video call, the RealTime Media Engine on the Chrome OS might display a black frame for approximately 1 to 2 seconds. [LOP-3207]
Calls might be blocked and the Connecting state appears in the tooltip while the RealTime Connector initializes. The blocked call leaves and open Skype window indicating that the call ended. The hang up button is unresponsive and you must use the X in the upper right corner to close the window. [LOP-3634]
In a call between two Windows users, if both speak at the same time, and one of them is doing software-based acoustic echo cancellation, one user might hear some echo. [LOP-3740]
Optimization Pack, does not appear in the Citrix Receiver for Windows Support Info generated from the Advanced Preferences menu. [608200, LOP-650]
If Citrix Receiver for Mac 12.0 is on the endpoint device and a Human Interface Device (HID) is removed after Skype for Business and RealTime Optimization Pack are running, the RealTime Media Engine might crash. 
Workaround: Upgrade your version of Citrix Receiver for Mac to a more recent version.
HDX RealTime Media Engine known issues
- In Seamless mode, the following issues exist for the Full Screen video:
Full Screen video appears in the letterbox format with the Linux version of the RealTime Media Engine in Seamless mode. 
The Full Screen Control hides behind other apps in a Seamless session in XenApp Seamless mode. 
During installation or uninstallation, it is possible to encounter certain error conditions where the error message string is not localized. [14530, 93]
- Sometimes, when attempting to install HDX RealTime Media Engine on Windows, a message indicates that there is no available disk space. However, limited space does exist on the Z:/ drive of the terminal. This issue is a known issue for Microsoft installers and applies to Citrix Receiver as well.
Third party issues
You might encounter errors with Skype (not Skype for Business) on iOS 9.2. [LOP-1313]
Workaround: Upgrade to iOS 9.3.2
Because of changes to the privacy policies in Microsoft Windows, audio and video calls might fail in fallback mode on VDAs. For more information, see Windows 10 camera, microphone, and privacy. [LOP-3460]
Workaround: Enable access to the microphone.
User1 might hear “underwater” (partially canceled echo) noise during the echo cancellation process. This issue can occur when User2’s microphone is sensitive to the input audio. [LOP-3742]
Linux might mistake some audio devices containing buttons for a Human Interface Device (mouse) instead of an audio device. When a user presses a button, Linux interprets it as a mouse button press and prevents the regular mouse from working correctly until the call ends. 
Workaround: Configure the Linux X11 graphics subsystem to ignore the devices as sources of the user input. Create or change a .conf file in the /usr/share/X11/xorg.conf.d directory with the following sections (for example, Jabra, Plantronics, or Sennheiser).
Option “Ignore” “True”
Option “Ignore” “true”
Option “Ignore” “true”
The microphone volume level of some Linux clients is low.
Workaround: Increase the microphone level using the Linux system volume control.
There might be a problem dialing dual-tone multi-frequency (DTMF) digits using a Jabra Pro 9465 device on a Linux client. 
Workaround: Use the RealTime Optimization Pack interface to dial the DTMF digits.
Citrix RealTime Optimization Pack does not support the Plantronics Clarity P340 audio device but does support the P340-M (Skype for Business qualified device). [597048, 603639,608218]
The microphone volume level of the Polycom CX100 speakerphone is low even at its full level when used with the HP Thin Pro client. 
Workaround: Change the registry key that comes with the HP Thin Pro by using the regeditor program on the client. You can run the program as root or from the Registry Editor component of the Profile editor.
These settings limit the range of available settings on the input volume slider. The RecordScale default value of 100 limits it to 25% of its maximum value for the microphone jack. Setting RecordScale to the maximum value of 400 allows the slider access to the entire scale.
Value name: RecordScale
Value data: 400 (Default is 100)
Value name: RecordScaleAuto -
Value data: 0 (Default is 1- sets to 100)
1 Sets the RecordScale value based on the hardware type.
2 Does not set the RecordScale value based on the hardware type.
For playback, these controls work the same way as the input volume controls.
Value name: OutputScale
Value data: 400 (Default is 100)
Value name: OutputScaleAuto
Value data: 0 (Default is 1)