I did notice in VLC media player "Stream 0" is type: Audio and "Stream 1" is type: Video. Whereas with the ones that work it's the other way around. Wondering whether that could be the reason audio doesn't play (but it does detect that video isn't the first stream...)?
Got it working. We had to change channels to Stereo and swap the video and audio streams and changed the bitrate from 44.1k to 48k. Not sure whether all of these were necessary, last one made it work finally but we had tried doing that without the other two changes in place and it didn't work.