itunes 12.4 artwork randomly not showing in songs view

I have finally had to abandon iTunes 10 (sob!) and have gone as far as 12.4.

I am not going any further - I've seen the disaster that is the artist artwork view in later versions and I'm not having any of it, but I'm very happy that 12.4 seems to have everything where and how I expect it, apart from randomly deciding some of my Films are now Home Videos, but I can fix that by editing media type in Get Info/Options. But there is one area of artwork 'misbehaviour'.

In Songs view, some songs show no artwork, despite everything having artwork in every other view (whether embedded, Apple/Gracenote provided, or manually inserted by me). At first sight it seems random but if there is any pattern it seems that:

- all 'proper' albums have artwork in songs view

- many single tracks (which I have defined as albums if, say, they are the only track from that artist) do not have artwork in songs view

- some sets of songs that I have defined as albums (e.g. two or more tracks on an old-fashioned single - what we used to call EPs, for those old enough to remember) do, and some don't, have their artwork.

So there may be some pattern, but it's hard to see any rhyme or reason when every other view - artists and albums - shows all artwork.

Anyone had the same and found a fix?

Thanks,

George