Next button doesn't work after Previous button used

Hi again,

I am struggling to get the next button to work correctly on this Infection control section now. It seems to work ok for me if I go through the section exactly as intended but the moment do click slightly differently the next button will no work. This issue is mainly on the slide 1.5 (the one with the big stop sign). My testers are struggling to get past this page and I can't seem to figure out what the issue is. I am wondering if it is a revisiting issue? It seems to work fine if you go through and don't accidentally or purposely revisit any of the pages but as soon as you do the next button won't activate. I tried adding a revisit variable but that didn't seem to help. I have attached the story file here for you. 

Also on a related note you will notice I was only able to get the previous button to work on slides not connected to a quiz. As soon as it hits a quiz a previous button will not function properly so I ended up just putting the previous buttons around the quizzes which works but it's ideal.   

Any help is greatly appreciated!  

Best,

Stephanie