Simulation not replaying properly

I'm working on a software training module comprised of several lessons.  Each lesson is built with several scenes:

1. The first scene describes a feature, why, how and when it is used.
2. The second scene is a self-running demo in which the student watches how the feature is used in the software -- on the first watch, it runs exactly as designed.  On the last slide of the demo, I've placed a button called 'Replay' that jumps to the first slide of the demo, to give the student an opportunity to watch the demo again.
3. The third scene is a hands-on exercise in which the student uses the feature in a way that is relavent to how they will use it in their job.  At the end of this scene they can take a short practice quiz to test their retention. After the results slide I've place a transition slide.  If they click the 'Next' button in the transition slide, they move on to the next lesson in the module.  Or, if they didn't do very well in the exercise, or they did poorly in the practice quiz, they have the opportunity to click a 'Lesson' button that jumps back to the beginning of the first scene in the lesson.

Here's the problem:  regardless of which button they click 'Lesson' or 'Replay', when they return to the demo, it runs completely irratically.  The timing is way off, running too fast and jumping from slide to slide sometimes missing slides altogether. 

Has anyone experienced this problem?  If so, does anyone have any suggestions to fix it?   I've looked at the possibility of refreshing or clearing memory, but don't see a way to do that.   I know that there will be many students who will want to repeat the lesson and/or demo, so this is important to my module.  It doesn't seem that I am doing anything that Storyline shouldn't be able to handle.