Storyline issue while reviewing quiz on safari

Hi all,

I have created an assessment module consisting five questions and a result slide.

When tested this on the Chrome browser it works perfectly. However it shows black screen when tested on Safari.

The steps I did are;

1. I appeared the test and from result slide I clicked review quiz button. 
2. It took me to the first question in review mode as expected. 
3. From this point I moved to second question using next button
4. I clicked previous button to come back to first one 
5. At this point screen went black. 

I can click on the onscreen continue button even this too is not visible.