Similar this to me. My sons camera, the nearly 4 year old one just recently stopped picking up sound. My daughters, the newer one works fine. It happened once and the mic started working on camera one when I picked it up, but it did it again a few days ago and so far can’t get it to come back. Have unplugged it, wiggled mic, etc. haven’t done anything to second camera but will see if it makes a difference. I figured first camera was just getting old and mic was failing.