Question Bank issue with iOS

Articulate Storyline: We have 3 question banks (each with a pool of 6 questions) in the same course. For each of the question banks if the user gives an incorrect answer (to randomly selected 5 questions), the quiz has to restart, with shuffled questions from that question bank. 

While this works seamlessly in Android-based devices, for iOS devices the program simply crashes - reloads / refreshes the browser page, after a few answers (8 to 10 questions answered). If we remove the graphics / media assets from the course, the program goes on for longer duration, but crashes after a long time (40+ attempts).

We have reprogrammed the course a few times from scratch, and everything seems to be in order. Is there any compatibility issue between the question-bank and iOS?