I am having the same problem others have described. Below is a detailed description and troubleshooting steps I have taken.
I work for a church, and we stream services through Switchboard Live (a multi-stream to Facebook, Youtube, and a generic webpage embedded player). The issue we are having is that when the audio is a single person speaking, audio on the stream works fine, but as soon as live choir or music starts, the audio starts cutting out. It goes completely silent. However, nothing is cutting out over the live house speakers. So this tells me it is not a problem with RF interference, microphone signal quality, our audio amplifier, or DSP/mixer.
The audio that is being captured by the PC and OBS is through a 3.5mm line-level analog mono plug. The audio comes from the church's live audio system with an analog output specific for our stream. I have observed the stream during a live service, and the times that it cuts out over stream, the audio signal on the OBS volume meter does NOT go flat - it continues to bounce and show uninterrupted signal activity. So this tells me it is not an issue with the live audio system or its signal output, OR signal input into OBS.
The problem is present in all stream platforms: Facebook, Youtube, and embedded player. So, I have tried recording our live audio and video capture in OBS to a local output destination (mp4 file), and the problem is STILL present in that recording (audio cutting out during music). So this tells me it is not a problem with our streaming service, or Facebook, or Youtube. It must be something with the computer itself, or maybe an OBS audio output configuration problem, a computer hardware problem, or a driver problem.
The computer is a fairly new Dell Optiplex 5090 with 11 Gen Core i5-11500, 16GB of RAM, integrated Intel video, Realtek audio, Windows 11 Pro version 21H2. I haven't always had these problems while using this streaming computer. The problem has only begun happening recently.
As an experiment, to circumvent the computer's integrated audio device and line-in jack, I got an inexpensive USB audio adapter with mic/headphone in, and plugged in our existing 3.5mm audio from the sound system. I added this alternate USB audio device into OBS to capture audio, and everything worked normally. However, last weekend during a service, the same problem occurred - single voice works fine, but music cuts in and out, just as before. So this tells me it probably isn't a issue with the audio input adapter or driver, because two distinct audio devices show the same problem. It may still be an issue with Windows 11 or computer hardware somehow, but I'm not sure what else to check there.
I'm starting to think it is a problem with OBS's audio capture and encoding. This problem seems to have arisen after an update to OBS earlier this year. Another problem I had after that recent OBS update is that OBS defaulted to a 48kHz sample rate, but the audio device in Windows was set to 44.1kHz. This mismatch caused issues with audio/video desync in OBS (lips moving on video didn't match audio). After I set both Windows and OBS to 48kHz, that problem went away - everything synced normally. I have also tried setting them both to 44.1kHz - it still works with no noticeable difference from 48kHz, but we still just have the problem with audio cutting out during music whether both are on 44.1Khz or 48kHz sample rate.
My OBS version is 29.0.2 (64 bit)