After 25 challenged users were connected to RDP service on Microsoft Windows 2012 R2, additional users could not connect over RDP.
This issue is caused by the Offline Authentication service.
Override the default configuration for the Offline Service to increase the number of current connections. This can be done by via a SYSTEM environment variable named RSA_DA_API_THREAD_POOL. Dev has tested with a thread pool of 400.
Launch the Control Panel on the machine with the Authentication Agent installed.
Navigate to System and Security > System.
Click on Change Settings.
Click on the Advanced tab.
Click on Environment Variables.
Add the RSA_DA_API_THREAD_POOL variable with a value of 400:
When done, click OK.
The new variable will show under System variables.