I had almost finished a design and was design-rule checking. I changed the minimum via hole size constraint to clear DRC errors relating to hole size errors. The next time I looked at the PCB, all the tracks had vanished. Pads, silk screen, GND plane etc are still visible. If I use the camera view, or 3D view, or export the design as Gerbers, pdf, png etc the tracks are correct and visible. I tried exporting the design as a json file and re-opening the json file - no difference. How do I restore the tracks? I attach screen shots of the PCB view )tracks missing) and the photo view (tracks present). I can send the PCB json file if someone can fix it. Thx - Charles