Reset Network. 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.
Reset Network Settings
If the mobile is off you should hold down the Power key for a short while to switch on the smartphone. If the phone is ON, simply start on step 2.
Go to Home Screen --> Settings.
Then scroll down the list of settings and tap General management.
After that choose Reset and Reset Network Settings. I then powered my phone off and on again for good measure. It worked!!!!
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