bug with the amazon music app
I have found a bug with the latest version of the amazon music app, If alexa hands free is enabled voiceover will sound like it does when on a call and become very sluggish. I disabled the hands free feature, closed the app and reopened and that fixed it.
It's not a bug, that's how they've now set it up. I did the exact same thing since i too use Voice over with the app. Once you turn hands free off, you just close the app and reopen it. Then it works as expected. The best thing to do is to call and ask them to fix that so future updates don't do that. Or you can also send them feedback.