Layers not revealed
Just wanted to post a discovery I made that might help others:
I was repeatedly having problems with layers (esp. in hotspots) showing up when clicked or triggered but losing my base layer. I reviewed my layer settings and triggers and everything checked out.
Then I realized that I had altered the background of my layers so that they were white and no longer transparent; this blocked my base layer content from being revealed. So if you can't see your base layer, make sure that you go to Design>Background Styles. Then select "no fill". That could help.