9.1 and before presented no problems when plugging a USB audio interface into the iPhone's Lightning port to record audio (5S and newer is capable of this, via an Apple USB-to-Lightning cable). However, 9.2 results in recordings that sometimes are peppered with artifacts: loud pops similar to the pops that are heard when said audio interface is initially connected to the phone (and when you interrupt a recording by playing audio in another app). I'm not a developer, so I don't know about proper channels for submitting this as an issue.
