This is actually related to the Plex Player (universally rather than just APV). Some of my content has multiple audio tracks (in the same language). e.g. I’ll have a 7.1 English track and a 5.1 English Track.
Almost all my users do not have the hardware to support the 7.1 audio track, but do for 5.1. Instead of playing 5.1 track, Plex transcodes the 7.1 track for them instead of selecting the 5.1 audio which can be directly played.