Were you trying to stream audio-only content (e.g. music), or is the issue about the audio part of a video?
The audio part of a video.
What kind of content (from where, online?) were you trying to AirPlay, in case that is a factor?
An online stream. I have done it with this stream for several weeks now except for last night.
Where you trying to AirPlay Screen Mirror, or doing in-app ‘basic’ AirPlay from the TV app, or iTunes, or QuickTime Player, or Safari?
Safari
Do you know what type of audio the source file has? Format, channels?
Not sure, but on a guess stereo.
Does it happen for other files/content as well?
Haven’t tried any other files as yet but I don’t see why it would only affect that one thing in this case.
I can’t replicate your issue (seems to work fine here), but maybe additional information is needed.