I just ran into the same issue and luckily found a fix quite fast.
It appears that if you have a widget in your viewport and you switch off the “Realtime” option (via CTRL+R) your widget will be displayed as long as you do not move it. When you move it, it will disappear immediately.
So in order to keep your widgets visible just keep Realtime on as they need to be drawn every frame when moved.
The aforementioned solution to switch on the FPS Counter might also force the window to refresh.