USB? The downside to Firesticks is that even though they appear to use USB as their power supply, they actually require the included Amazon USB power adapter due to a slightly higher voltage/amperage requirement.
When I tried to use Amazon Music directly on either of my Denon receivers, I would get the same issue from time to time, even if I used the horrible HEOS app on my phone. I essentially gave up and use the Amazon Music app on either my Roku or Firestick. The Firestick does support Amazon Music's...