Information
This setting ensures that users & administrators who Remote Desktop to a server will continue to use the same session - if they disconnect and reconnect, they will go back to the same session they were using before, preventing the creation of a second simultaneous session. This both prevents unnecessary resource usage by having the server host unnecessary additional sessions (which would put extra load on the server) and also ensures a consistency of experience for the user.
Solution
Set 'Restrict Remote Desktop Services users to a single Remote Desktop Services session' to 'Enabled'.