As it turns out, there were some pretty serious glitches related to the bubble shield difficulty settings. If you turned on "healthy pop," it worked properly with enemies, but something happened with things like archer arrows and saw blades - oh and mini bosses. I've reprogrammed it to work properly as a second health with "healthy pop" selected.
Also, I changed the text in the Game Over menu from "Return to Start" to "Return to Hub," which I think better explains what you're selecting. I was between "Return to Hub" and "Try Again."