It solved my problem - which was very low volume after Android Pie update (9) on Samsung Galaxy S9. I had just purchased new wireless earbuds and was set to return them when I stumbled across this fix.
Do anyone know if this issue been fix yet? I've experience the same thing and completed most of the troubleshoot found online just short of factory reset. I'm using the North American Unlocked Galaxy Note 9 (8 GB/ 512 GB). Bluetooth volume is so low that it's unusable. Fortunately, this phone comes with a headphone jack. I just started connecting my bluetooth headphones to my iPhone X with no issues. Two pairs of mid/high end headphones ($100-$300 range), my automobile (2014 Nissan Altima), and still the volume is too low on my Note 9. Even with the volume turn to max on both product and phone. No issues before the pie update.