Your first pic is the Display View, and it shows the generic MC icon, which means that track does not have cover art associated with it. Even though one typically thinks of cover art for an entire album, MC allows you to assign unique cover art to each track if you wish. To learn more about how cover art works, where it is stored, etc. Check these two things:
See: Options/File Locations/Cover Art
See:
https://wiki.jriver.com/index.php/Cover_ArtTo select among the different options for what you can show in Display View, right click on that big blank area, and you will get a menu with a number of items you can pick from, including cover art. I am pretty sure you already have cover art selected, but as I stated above, it would appear none is associated with that particular track. Again, check out the link above.
As for your 2nd pic, you don't see the cover art in mini display view in the tree for the same reason... no cover art is associated with that particular track. Navigate to the full album that the track belongs to, and show all the tracks. If one or more of has cover art associated with it, right click copy the one you want to use, and paste it onto all the tracks for that album. If none has art, then you will have right click "get from internet" or manually search for a cover art .jpg manually (and paste that onto the album). Read the link above, experiment with a handful of albums, and you will start to understand how it works.