I am having this same problem with my Galaxy J7 Star. The problem started immediately after the Tmobile update a few weeks ago.
The apps are not open when I start the car, but the music starts to autoplay. It used whichever music app I last used; for me it's Amazon Music or Spotify. It happens even if I haven't used the music player for days.
The app doesn't physically open on my phone, so I can't even shut it down from my phone when the autoplay starts.
If I pause the music in my car to make it stop, as soon as any other audio comes through the car's Bluetooth (navigation, text message that the car reads to me, etc) the autoplay starts back up. It's a safey issue because it scares the heck out of me every time! It also wakes sleeping children in the backseat of the car.
As I said, this began with the most recent update. I've had the phone and the car for almost a year and never had the problem before. WHAT IS THE FIX?
I wondered if you found a fix for this problem. It started for me right after the latest update. It happens with Amazon Music, or Spotify, or whatever is the last music app I used. Even if I haven't used the app for days, it will still start autoplaying in my car. So frustrating!
This is not an app issue, this is a samsung issue. The apps play music without even being open as soon as bluetooth connects. Its almost as if they run in the background and pick up where they last left off with a song or whatever.
Where is the fix Samsung? Months of complaints resulted in nothing yet