Quizzes and Lessons containing MP3 files cause the Moodle Mobile app (3.4.2 and 3.5) to unexpectedly crash on iOS devices. This behavior has been noted on the Moodle for Mobile forum here and [here|https://moodle.org/mod/forum/discuss.php?d=371943.] The behavior doesn't occur each time an MP3 file is played. In my experience it is somewhere around the 4th or 5th time an MP3 file is played that the app crashes. After the first crash, the app will close each time an MP3 file is played  

To replicate this problem, follow these steps:

1) Create a quiz (or lesson) 

2) Create a question containing an MP3 file and duplicate 4 times so that there are a total of 5 questions containing MP3 files in the quiz.

3) Attempt the quiz using the Moodle Mobile app.

4) Use the 'next' and 'previous' buttons to navigate between questions, each time making sure to play the MP3 file. 

5) After a short time, the app will suddenly close. If the quiz is re-attempted, the app will once again close.