I'm experiencing the same problem and after much experimenting, came to be using the same workaround as the original poster. I'm glad it's not just me. Following this issue in the hopes of a solution in the future.

I'm wondering if the OP or anyone else found a way of detecting if the audio has changed to be quiet/loud. The category/mode/options all stay the same and there doesn't seem to be an overrideOutputAudioPort property on AVAudioSession. I'm trying to detect if it has changed, and if it has, trigger the fix to return audio to normal volume.