I am the person who created that sentence.
What I was able to discover is multiple issues incorporated by Citrix into security patches or enhancements in their client product.
These cause instability and loss of compatibility that limit operability or scalability.
Citrix Workspace in its most modern versions and still maintains backwards compatibility with legacy servers.
The specific version indicated is the one that we have detected as the most stable version into the most updated versions.
Subsequent versions from 19.12.2000 LTSR Cumulative Update 2 they started having new problems.
Some previous versions work, but the best stability and load capacity is not achieved.
It is possible to use Citrix Receiver 4.9, but we have found some functionality that does not work very well for load simulation, but you can try to use that.
For load testing, the better version for now is 19.12.2000 LTSR Cumulative Update 2.
The problems are Citrix Receiver and Workspace, problems that they have introduced by Citrix.
The problems affects any type of tools that use the Citrix client for automated tests or for load testing.
I don't know if the answer is what you expected.
If you have any other questions, don't hesitate to ask.