Can you try to clear storage and cache, then re-setup Libby? I’m trying to sort out what is different between your situation and mine.
Also, can you try another media player and see if the same poor experience is there?
Also, you do have microG enabled, correct? All the microG “checkboxes” are active under the “self-check” (System Settings > System > microG)?
OK another question: when it was playing and you couldn’t stop it, was it showing in the dropdown notification? My suspicion is there is a permission somewhere that is preventing it from showing there, so please confirm.