Does your course have an Engage element inserted as a tab, more than likely a glossary?
Articulate Presenter is designed to pre-load the next few slides. This is why you typically only see the loading bar for the first slide. (Makes me wonder,then, if you use hyperlink navigation in the slide, and don't go through the slides in their natural order, how would Presenter know what slides to pre-load?)
I don't believe that Engage interactions does not pre-load. This is why you see the loading icon, a wheel this time, whenever you land on an Engage slide. Frankly, I've gotten to the point where I don't use Engage, except for a glossary tab; I don't like the change in appearance and navigation method. (Sorry, Jeanette.)
But when the Engage interaction is a tab, like a glossary, it has to load along with the first slide. It caused my course (with a huge glossary) to bog down, sometimes never finish loading at all (overfill the buffer?). Moreover, I wonder if the Engage glossary re-loaded with every slide advance, because all of my slides were bogged down.
I removed the glossary and republished, then loaded that onto the Galaxy and it worked just fine. Now I'm only using the Galaxy to demo to a prospective client where a laptop would be inconvenient to carry around, so I can live without it.