What exactly do you mean with "Avatar"?
Is this the cover art picture that you can see in Mp3tag in the lower left corner like this:
Can you refresh the view of the folder in Rekordbox, maybe in some context menu or by removing and re-adding the folder?
Maybe this hint can help you:
(If you can see the cover art in Mp3tag, there is not much we can help here in this Mp3tag forum for your Rekordbox problem.)