First of all, check the power settings on client and server side, they are usually at cause.
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.
If you are experiencing this issue with the HTML5 web client, edit the settings.js file with notepad located in C:\Program Files (x86)\RDPlus\Clients\www\software\html5
and modify the W.send_logoff = true parameter to false.