When working with multiple levels, you may have come across times when the objects in your drawing become pretty much invisible in the 2D view, only showing a dashed outline, like this:
Don’t worry that your drawing is broken, it is just a way of controlling which level objects belong to, and to maintain visibility when working.
It all has to do with which level is currently the active one. In the example above, the active level is the Base, which does not contain any objects. Changing the active level to Level 1, however, will show the objects that are placed there:
To change active level, simply right-click the desired Level name at the bottom of the screen, or select it in the Level overview.