Can't go backward in quiz with custom back button

Problem

• When answering quiz-pages, the "correct answer" layer will go to the next slide automatically. So the user is answering one question after the next, until the result slide
• Using a custom back button (back to last slide) the user can go backwards and see already answered questions
• When going back 2 times, onto answered question slides, a blank/white slide is shown. From then on, the navigation is not working properly anymore.

 

The file is set up as follows:

• intro
• X quiz questions (multiple choice, drag drop...)
• one result slide
  
  
• Storyline 360 and html5 export is used 
• the master slide has a complex set up of variables to create a progress bar and check, how far the user is allowed to proceed in the presentation (only until the next unanswered question)

The master slide holds the custom navigation, including the back button that gives us trouble. So the back button is on the master slide.

Solutions tried:

1. we tested to place the button on the slides themselves, instead of the master, still didnt work.
2. we tested to use back buttons on each slide with a fixed slide the button will lead to, not just "back to last slide" (lots of work, but well...), this also didn't work.

We thought it was something with the layers that auto-skip to the next slide maybe, but we need them for the auto-advance. Since it's also a quiz the option to reset slides on revisit is not possible we think.

Also maybe it's a drag drop issue, we had some trouble with drag drop slides in the past.

 

Strangely, it did work in Storyline 2 with chrome html5 export.

 

Any ideas?

Thank you very much in advance!

We can't share the file here directly, but I could email it to support if kept confidential. The attachment is just a mockup to show the general page setup.