The default Loginapp page templates search for maintenance messages without a "Location" parameter. Thus, when adding a maintenance message with a "Location", the out-of-the-box Loginapp (JSP) will never display it.
To make the Loginapp to use a location parameter, you need to change the Loginapp (JSP) template files. More information on how to customize the Loginapp (JSP) pages can be found here: Customizing UI (look and feel) of the JSP-Loginapp .