You didn't mention that you were shooting in discreet mode. You have three options: discreet, PiP, and Split. Discreet creates two files while PiP and Split creates one merged video file. You can change modes by pressing the top right icon.
Also, when I get one AirPod not working, on either my watch or my iPhone, I use the volume controller to turn up the volume. This resets it, then turn the volume back down.