The last update installed a Media Volume Limit on my phone. Even when the option is deselected and turned off, it still affects the output of my phone when connected to Bluetooth or Android Auto. It sets the output automatically at very low levels, even when turned off, and renders the volume buttons on my phone useless. I move to volume on my phone up and down and nothing happens. The only control over volume I have is through the stereo, with no real output from my phone. It effects all frequencies. I have no bass, midrange, etc. All output is squashed. I have reset network settings. I have done a complete phone reset. My phone says all software is up to date. A couple of people suggested the Good Lock App. with Sound Assistant. I finally found which one and downloaded it. There is some difference, but very little. It does not resolve the issue. Everything still sounds muffled. I am still not able to adjust volume output independently on my phone when connected to Bluetooth or Android Auto. Samsung Customer Support has been no help at all. They even deleted my previous post even though I used no profanity, and the words were bleeped out any way. I've been a Samsung Customer for a lot of years. This experience has me ready to jump ship.
In order to see if a 3rd party app is interfering with the connection or your controls in some way. 🙂 You could try it.
Did we look into Absolute volume?
Do you have developer options enabled?
For Safe Mode, from the power menu, press + hold Power down on your screen until the Safe Mode option appears.
Go to Settings>About phone>Software information>quickly tap Build number until you see a message for Developer mode being enabled. Go back to your Settings>Developer options will be at the bottom. Inside, there should be an option for Absolute volume you can toggle to see if it might work.