Base Layer objects no longer visible behind New Layers

Thanks for peeking in, Sheila, but that isn't the issue. 
I actually checked there first, because I use that menu a lot to decide whether layers replace each other or progressively add to each other using the top check box, so I knew it existed.

I almost always have some of the bottom layer showing, and often leave trigger buttons for other layers showing so that users can jump from one to another instead of having to always go back to the home layer first. 

Something new is happening that creates a blank white screen as soon as I hit a new layer.