[Gracus]

As you can see on the screenshot I posted: no cdart and no album cover grab from fanart.tv (the displayed cover come from the file tag)
On fanart.tv, there is for "back in black" (the one that was on my screenshot): 4 covers and 6 cdart

But as you can see, none of them are grab (same issue for other album that I know they have covers and cdart on fanart.tv) :

Might still be that the musicbrainz album id is wrong. From what I recall Picard by default inserts the releaseID which limits to the specific localized media while the releasegroup is the album itself.

To test, simply open your music DB with a tool like "SQL lite browser" and check what the value is for the musicbrainzalbumid for that specific album.
Also as another test you can clear the value in the DB so it's empty. Save the DB and use the contectmenu to perform another auto lookup.
If the artwork is found, it's definetely an issue with the wrong musicbrainzalbumid.

Here are the AlbumID I got:

tag: f7c680af-5b09-3fea-be84-5e00a7da56a0
db: f7c680af-5b09-3fea-be84-5e00a7da56a0

I remove the value from the db and launch an automatic search for artworks and still no cdart