I noticed the low volume issue, too, but I chalked it up to using AirPod Pro and not a proper pair of headphones.

I had another Bluetooth-related quirk, probably because I used earbuds. I didn't pause the TV show or Bluetooth connection before I went to the bathroom. I kept hearing the audio as I walked a few rows (maybe five or six rows), before the Bluetooth connection likely disconnected. When I got back to my seat, I didn't regain my Bluetooth connection. I tried disconnecting and reconnecting my AirPod Pro, and, despite it saying I successfully reconnected each time, I could not hear any audio.

I eventually gave up and asked a flight attendant for a pair of the freebie headsets. It's most definitely user error or an odd edge case, but I wonder now if I could've successfully reconnected to another seatback and heard the audio fine then.