I don’t have an Amazon Unlimited subscription, but I do have Prime. I also have quite a lot of purchased music, mostly gained automatically through buying the CDs but also a few I have purchased digitally through Amazon music.
Now, when attempting to play these purchased albums through Sonos (S1), clicking on them does not display the tracks. Attempting to play them does not add them to the queue (it shows as “Not In Use”) and the tracks are played in a random shuffled order.