If you are referring to the album artwork that shows when a song is playing, I have noticed that what displayson the lock screen might not be the same as what is currently playing. For me, probaby 80% or more of my library doesn't have artwork, so I just attributed it to the current song not having artwork, so it left the last artwork it had up, but I haven't done any thorough testing to verify this. Could it be that you are seeing the same as me?
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