Comment by anentropic

I used to experience this all the time and had a 3rd party app installed to lock the balance to centre.

But it seems to have gone away in last couple of versions of macOS, have not had the 'fixer' installed since I got an M1 and it hasn't occurred again for me (so... Sonoma and the one before).

If I recall, the original reason for the bug was a stupid keyboard shortcut (helpfully mapped to "f*** up my audio balance") that was easy to trigger by accident, with no visual feedback to know that you'd done it.

I wonder if it's locale-specific, maybe some keyboard layouts or whatever still have it mapped.