On one of my computers, the NetWorx graph does not display in the taskbar widget. I have the "Display the Graph" option enabled in the Taskbar Widget Settings. The widget does display the up/down numbers, but not the graph.
A missing graph (or any other enabled widget element) simply means that your taskbar widget area is too small to fit it in. You can easily resolve this issue by resizing the widget:
Move your mouse cursor over the left side of NetWorx widget - a vertical bar will appear. Click on that bar and, and while holding the left mouse button down, move the mouse to the side to resize the widget area until all enabled elements are displayed.