When using the roadway optimiser, the model window remains blank (i.e. black) after calculating, changing views, orbiting, panning, anything.
The only thing that forces it is to resize the overall optimiser window by dragging an edge.
This is possibly a graphics hardware acceleration issue. Before i explain the fix, you can also try the little "Display Options" button at the bottom of the screen and set it back to "High Quality".
Re: Hardware Acceleration
Try to "disable hardware acceleration in dialog viewers" from System Settings - Advanced - Render Tab as shown.
You can also see the KB article here
Yes, something like that must be related - however
Strangely enough, sometimes turning Hardware Acceleration ON can fix. All graphics systems are different.