I'm seeing the same issue, only on PC. Works great on mac's version of Chrome. Curious if it's me or something in Edge Animate.
Know issues of Edge Animate: http://helpx.adobe.com/edge-animate/kb/known-issues-edge-animate.html
there is: Webkit (Safari, Chrome) browsers-only: Responsive scaling with symbols breaks element z-order when viewport is larger than the Stage. (3632270)
The missed symbols are showed after re-size the browser window to a 60% or less
on Chrome, Tablet version for Nexus 7 it works fine.
I was able to work around this by breaking up the main large background JPG (was 2x the size of the stage). I broke out all the individual objects into separate PNGs, and imported them all into the symbol. This solved the issue for me. Hope that helps someone else.