I have an issue with external audios and images in questions. I've confirm the problem in Android 6.0 and Moodle Mobile 3.3.2. In iOS 11 the app is working fine. I've also check the problem in Android 7.0.
So, in the first attempt of a question I can see the audio and image which are linked to an external url. Then, when I check the answer I loose the audio and the image for the complete quiz, not only the question. If I finish the quiz and try it again the audio and images are still lost.