Could you post a video of your issue. For me, drag the fence beyond the task bar is difficult since it will snap to the taskbar top when you get close enough to the taskbar. So moving it under the taskbar is difficult, unless you intentionally want it to move beyond the snapping point.
I posted a video from what I see when dragging Fences down. As you can see from the video. The dragged Fences will first snap itself to the taskbar when it come close with it. It won't move further down, unless you keep dragging down.
Stardock Community Assistant