I saw the same issue with Android 8.1 when using Apple Music. What fixed it for me (I'm getting artist/title, but no album art yet) is go into settings and find the battery optimisation page. Disable battery optimsation for bluetooth (I think theres bluetooth and bluetooth MIDI) and Play Music (or whatever app you're using for music.) You can also try enabling developer settings and within the developer settings changing the AVRCP version to 1.3.
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