Serious audio mixer issue in Studio Mode affecting live streams

Operating System Info

Windows 10

OBS Studio Version

28.1.2

OBS Studio Log URL

https://obsproject.com/logs/CWJaJI4u2sKlRuC3

Expected Behavior

During live streaming in Studio Mode while switching back and forth from a "camera only" scene to a "thumbnail camera + video" scene the audio source can be monitored and heard in the recording and live stream while appearing in the audio mixer. Switching back to a "camera only" scene the audio can't be monitored and heard in the recording or live stream while not appearing in the mixer.

Current Behavior

During live streaming in Studio Mode while switching back and forth from a "camera only" scene to a "thumbnail camera + video" scene on an intermittent basis the audio from the currently played video will disappear from the audio mixer and the audio can't be monitored while it being still outputted in the recording and live stream. When you switch back to a "camera only" scene the audio of the Media Source appears in the mixer and is now monitored but can't be heard in the recording or live stream.a

Steps to Reproduce

1. Create an individual scene per each guest and add a browser source as their camera/mic
2. Create a scene "Video Player" with multiple Media Sources, add a video with audio for each
3. Create a scene "Cameras" with each guest's camera scene
4. Create a scene "B-Roll" and add each guest camera's scene from step 1 and the "Video Player" scene

** From here it's random if the bug will happen or not and it's not clear what triggers it, it's been happening for more than a year and I've never been able to reproduce it off stream which makes it really hard to report here.

5. Toggle on and off the Media Sources (I use a Streamdeck but use whatever you have) while the guests are speaking and between some videos switch back and forth within the "Cameras" and "B-Roll" scenes.

Anything else we should know?

This is a long term issue which have been impacting our live productions negatively. This issue was happening on OBS 26 and 27 versions as well.

There's another version of this issue that happens less frequently where you would start a Media Source and the video will work whereas audio can't be monitored, heard in recording or live stream and doesn't appear in the audio mixer. Only started happening in OBS 28.

Fingers crossed this one will be fixed asap.

Start with the attached OBS log and the Studio Mode reproduction steps for the Cameras, B-Roll, and Video Player scenes. Investigate the intermittent Media Source audio behavior across OBS 26–28, focusing on when mixer visibility, monitoring, recording, and stream output diverge. Done means the audio remains consistently available in the expected outputs when switching scenes and toggling Media Sources.