Is all cover art within a specific album missing or is that some are missing?
If the latter, you should check iTunes. Could be that the album art is only assigned to the first song of an album, but not to the rest of the songs.
To verify, right-click on a song, select "get info" and select "artwork".
2004 e87 118d (ret.), 2007 e92 330d (ret.), 2007 e87 130i M-sport (ret.), 2009 e92 M3 (ret.), 2010 f10 535d M-sport (ret.), 2015 f10 M5 CP (ret.)
2017 f82 M4 CP & 2009 e70 X5 35d