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At times, in order for your Spotify account to run with no interruptions when connected to a blue-tooth device, it'll be necessary to clear up the connection between the account and the device.
To solve this issue, can you please try the following?
Making sure your Spotify account is currently not accessed on any other device. You can also check this support site article and the section 'Log out everywhere' to make sure your account will be accessed by no device other than the one you'll use in connection to your car blue-tooth audio system.
Making sure your car blue-tooth audio system is not connected to other devices except for the one through which you use your Spotify account with.
Let us know how it goes. We'll look out for your reply and get back if you need any further help 🙂
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I have had the same issue for many months now. I finally found a workaround.
I am able to play music with great playback on the Android Auto app! This workaround is less than ideal. The Android Auto interface is overly simplified and irritating at times, but the Spotify works! Install the Android Auto app from the Play Store, set the app up, make sure Spotify is running in the background, and connect as normal. I hope this works.
I am using a Razer Phone 2 connected over Bluetooth to a 2017 Ram 1500 with Uconnect software.