Thank you very much for the repro- with this I have narrowed down the problem a bit more, and it appears to be caused by the iOS media service being reset. I am finding I can reproduce this issue in any FMOD application by hitting the “Reset Media Service” button in the iOS Developer settings application, which sends out this this notification: AVAudioSessionMediaServicesWereResetNotification.
When this reset event occurs, the audio session is invalidated, and the only thing you can do is to reinitialize all of your application’s audio objects, as you are doing. It is not clear to me why this reset notification is suddenly showing up more frequently- we have had a few other reports of this issue now; but it seems the only workaround at the moment would be to handle this media service reset when the AVAudioSessionMediaServicesWereResetNotification occurs. I have passed this onto the Dev team to explore the possibility of handling the reset notification ourselves, or at least adding some documentation on what to do to handle this situation. In any case, thank you for your assistance with investigating this issue, and thank you for bringing it to our attention.