The notification popup that appears when sending a notification from the terminal with notify-send is always empty. However, when I wait until the popup goes away and then click the "i" icon in the tray to reopen the message, the text is shown.
This is because new notifications aren't showing title. Try to run: notify-send "some title" "some text"
That works. But the behavior is still odd. The body is an optional parameter for notify-send and therefore it shouldn't be required for meaningful plasma notifications. If no body is given, the summary should be displayed at least. This BTW was the default behavior before 4.10, but now it has changed.
https://bugs.kde.org/show_bug.cgi?id=307670
*** This bug has been marked as a duplicate of bug 307670 ***