Editing a system made up of 9 note lines I decreased space between note lines trying to get a two systems per page layout. Reaching 3.0sp (guess that's the point where two systems fit on a single page) all the pages disappear. They again appear on increasing that value.
Comments
I can't reproduce. Could you post a file to reproduce?
You might want to reduce the scale to fit two systems in a page in Layout -> Page settings
After saving and reloading it now works....