Storyline's loading "spinner" - how do I ensure it appears?

OK - In dealing with another issue (i.e., HTML5 content on iPads loading very slow...see thread here), I am trying to do a sort of workaround and I could use some help.

I have created custom previous/next buttons. When running the course on the iPad (HTML5 version), and I click my custom next button - it shows my "selected" state, and the current slide just sits there...seemingly loading the next screen (which takes 10-15 seconds). However, I have no way to tell that anything is happening for those 10 seconds...it just sits on the current screen and it looks frozen. The loading "spinner" does not appear. 

As a workaround, I created a new layer that has the word "Loading" on it, and now my next button takes users to that layer, which is set to advance when the timeline ends. I'd rather not have to do this workaround. 

In a couple other courses I created (also HTML5 on iPad), the loading spinner DOES work when going from one slide to another for some reason. On those courses, I used the native previous/next buttons...is that why the loading spinner works for those courses and not my new one with custom previous/next buttons??

Anyone know? 

Thanks...