Hi,
I fixed this problem on my husbands phone in a really unusual way. I put the phone into developer mode and disabled automatic routing to usb audio peripherals and bluetooth audio peripherals. Here’s the unusual part: The phone was second hand and the neighbours bought a new car. The new car was a make it had previously shared a bluetooth and USB connection with. Even though blutooth was off the ‘automatic audio peripheral’ function seems to have divided the phone’s audio potential in anticipation of connection.