In the AdminTool, click on the Server tile and click on "Group Policies (GPO)" You can set up a timeout for disconnected sessions which will cause a disconnected user session to automatically logoff after a while. 

- if you want your disconnected sessions to terminate quickly, type in 0.5 for 30 sec. - enter 0 if you want your remote sessions to never end.

If your server is the member of a domain, this strategy may need to be set directly on the domain controller. 

- open your domain strategy object editor (gpmc.msc) 

- and locate the following strategy: Computer configuration / Administrative Template / Windows components / Remote Desktop Services / Remote Desktop Session Host / Session time limit /

You can also make sure your domain controller do not prevent local strategies to be executed. 

- this strategy needs to be disabled and is located in: Computer configuration / Policies / Administrative Template / System / Group Policy / Turn off Local Group Policy objects processing. 

Either solution should work, please choose the one that fits your preference.

If you are experiencing this issue with the HTML5 web client: 

- edit the settings.js file with notepad located in C:\Program Files (x86)\TSplus\Clients\www\software\html5 

- and modify the W.send_logoff = true parameter to false. Please note that if your TSplus server has joined a Domain, then TSplus disconnected sessions rules don't apply.