I’m using Acer 14 Chromebook with the same issue when using the Android app for Plex- when playing a video with 5.1 audio the voice channel is either missing or at an very low volume level. This happens also on streaming live TV audio that is broadcast in 5.1 audio.
This problem does not happen if I use the browser and web instead of the Android app.
This problem does not happen when using the Android app on my Samsung Galaxy S9+.
