Electronic echo/distortion only audible on YouTube

[mishakim]

During a livestream of our church service last Sunday, at various points, the audio in the YouTube stream became massively distorted. It started quietly and quickly built up to overwhelming. But, I didn't hear this at all in the monitor output. I've linked to a clip exhibiting the problem, it starts at about 20 sec. I'll see if I can get logs on Sunday, no-one should have used the computer since last time, but I'm not sure.

What I'm hoping for is, can anyone listen to this clip and tell me from the noise, what kind of noise it even is, so I can track down what's causing it?

There are two Rode M5 microphones in the sanctuary going through a Motu M4, and the lavaliere you see the pastor wearing is an analog Shure (new mic, old belt pack) going through a Bose ControlSpace-based PA system that then goes to the Motu via the Line In. There are two lectern mics also going through the PA, and I don't think they were muted. The Motu is connected to an Apple Silicon MacBook Pro via a Thunderbolt dock. I mix the PA and the Rode mics in Performer Lite, and output that to OBS which combines it with video and sends it to YouTube. I was monitoring the PL output, rather than OBS, since I can not reliably get OBS to actually provide monitor output, so I think the problem is occurring either within OBS or in YouTube. Once it was brought to my attention, I muted the PA system input, and used only the Rode mics, and the noise went away. Later I was able to unmute the PA and it was fine for a bit, but eventually the noise came back. No one heard the noise in church, including on the FM loop that is getting the same line out from the PA as the Motu.

PS - I'm not an audio engineer, I'm a patent attorney with lots of experience with audio technology, but not live sound mixing.

 

[mishakim]

I now have logs:
https://obsproject.com/logs/aPIkVVAIERN5oOvA (old)
https://obsproject.com/logs/6semZU9XLf5mplkP (today, when it happened again)

Today the problem started during a piano prelude, some time after the music started, and quickly built up to intolerable. I stopped and restarted the stream and it was better for a while. It came back during the sermon, and I was able to fix it by switching to a different audio source and back. Then it happened again during the postlude, and I wasn't able to do anything about it till it was over.

One clue, OBS sampling rate is set to 48, and is greyed out. Performer Lite was set to 44.1. Since I couldn't change OBS, I changed it in PL, but not till after the service, so I won't be able to test if that was the problem until we have another service.
Second clue, the problem is audible in OBS's own recording of the service, so now I know it's not YouTube, it's something within OBS.

The OBS log analyzer says I've hit Max Audio Buffering, and I'm trying to understand what that means from the logs. I see messages about it, like this:
11:06:35.121: adding 576 milliseconds of audio buffering, total audio buffering is now 960 milliseconds (source: Organ-NDI)
11:06:35.121:
11:06:35.144: Source Organ-NDI audio is lagging (over by 280.71 ms) at max audio buffering. Restarting source audio.
This certainly seems like the problem. The thing is, I'm not using audio from that camera (or any of my NDI cameras), I'm only using audio from the M4. There are also a ton of error messages about being unable to reach my internal RTMP server, which I'm also not using. I'll remove that source.
Do I need to remove the audio channels from the my NDI cameras? How do I do that?