Your license allows more than 2 users, however TSplus allows no more than 2 concurrent connections.
1 - Please update your TSplus to the latest version, reboot the server and try again.
You can get the update here : https://dl-files.com/data/UpdateRelease.exe
Make sure no users are logged in before installing this update, you can check for remote users by launching a task manager and clicking on the users tab. Disabling your anti virus is also recommended.
Make a scan exclusion rule on C:\wsession and C:\Program Files (x86)\TSplus\UserDesktop\files and make sure your users have sufficient rights to read and execute all programs in these folders.
2 - If it still doesn't work, then it means that a Windows update has impacted the RDP connection module and has overwritten the TSplus settings.
- open a DOS command prompt as administrator
- navigate to the tsplus\userdesktop\files installation directory (cd "c:\Program Files (x86)\tsplus\UserDesktop\files")
- run 'svcac.exe /updatekernel'
- after the popup, open the Windows Services Manager
- open the Wndows Service Manager
- restart the 'Application Publishing Service (APS)' service. Two services will also be restarted
After that you should return to normal operation in multi-session mode.