I had this issue with web browsers not outputting sound to the stream after I updated to a 31.x.x version (specifically 31.0.1). I also reverted to 31.0.0 and still had the issue, seems to be a 31 introduced issue.
I do not use Desktop Audio, I have all tracks unchecked for it. Instead I control each audio individually for my entire setup (it complicates it and gives me more control). There are 3 browser sources that did not work properly after update. I think that is all the browser sources I use that have audio associated with them...
I normally have them set to Monitor and Output, which is what got borked! When I tested Monitor Off, and you can hear it on the stream output side just fine, but I won't hear the alerts live (which is the whole point). I tested with monitor only, and that worked as intended. It seems Monitor and Output simply doesn't output for me, it's basically another monitor only option. The funny thing is, the Audio Mixer will register that the web browser is playing a sound, and the audio does not output to the stream.
I reverted back to 31.1.2 and it worked flawlessly.
If you are also getting this issue, this was the simplest way to fix it, downgrading.
