I've tried with a basic action to "set" the visibility, but it doesn't seem to update on the fly.
If you want to dig deeper, as to why your basic action fails to update the hotspot I recommend turning on debugmode, assigning a logkey and spreading some debugvar(varname) or also debugvar("yourstring") here and there so you can see what works and what doesn’t.
I've tried (and updated) mine above and it works. It may impact rendering performance.