Issue with LMS Next and Back Button - animations

Good afternoon all! 

I am currently using Articulate storyline 3 to create courses that I then put on my LMS (as a scorm file). We have had some students having issues with the next button not appearing even when they click on the animations that is supposed to trigger it appearing.

We believe it occurs when the learner clicks the back button and goes to a slide that requires animations to be clicked before the next button appears. The first time they see the slide, the animations work and they can see next, but if they click back, when they do the animations again it does not appear. We have been able to replicate this issue on the 'Recognition of shock' slide. After clicking the back button on the 'Management of shock' page, I reclick all the boxes but a next button does not appear as it should.

I have attached the storyline file :) 

Not sure what is causing this. Any help is very much appreciated as this is causing some understandable headaches for our students

Thank you in advance guys!