I created a new project, added a navbar and a couple of sections, and then I found that I cannot scroll down in the main view window to see the sections. I don’t see a scrollbar.
There’s a scrollbar to the right hand side, make sure you have enough elements on page to warrant a scroll bar appearing and that the Projects Pop Up Window is not obscuring it.
You can also use the mouse wheel if you have one, just click on design pane and scroll up or down.
It’s also worth using the screen selector to view in different sizes to see if it appears.
Failing that, not sure what else to suggest.