>Where in the code would I look at the buffers?
All the buffer code is in the ContinuousAudioUnit module. The buffer callback is at the top of the implementation. Unfortunately it isn’t the easy implementation to get to grips with since it’s in C and has a custom ringbuffer, but I think I would just focus on the callback and the initial configuration in OpenAudioDevice.
You can also try experimenting with the settings in AudioSessionManager and research whether there are any particular pitfalls with certain audio session settings other developers are encountering with AirPlay.
I forgot to ask — are you sending any messages to the shared audio session anywhere? This is a very common cause of issues like this. You can check by doing a case-insensitive search for “audiosession” in your code.