Mine does that when I had been playing a video or reel and didn’t mute the video again. When autoplay is active with sound on the Facebook app, it mutes whatever other audio you’re playing. That’s been the case for a while now. I just mute the videos and restart the external audio and all’s good.This is not the first time Facebook has been using the audio API to do background processes. A good proof is that when I am playing music over AirPods and open the Facebook app it often stops the music.
I deleted FB for now.