Thanks, I see them now. FYI. There's no need to use invisible buttons with the current version of in5. The content itself can be a button.
The issue here is that in5 v3.5.4 is smarter than v3.4.1.
It recognizes that this Appear animation is set in such a way that it plays the opacity in reverse (from Current Appearance). So in5 determines that is content is to be hidden after animation (when hidden, the button won't work). If you change the Opacity setting in the Animation panel to "Fade in", everything works as expected because the button goes from invisible to visible. None of this is obvious because the button is transparent. ;-)