iTunes is not displaying the correct artwork for certain tracks

I have a track in .mp3 format that I have imported into an album in iTunes.

I go to 'Song Info', edit the various fields to correct errors (such as year of release) for each track, and add the relevent artwork - but the artwork isn't what I've selected and saved for certain tracks.

In 'Song Info', the correct artwork displays, it is just in the list of tracks in that particular album it is wrong. If I delete this and click on the correct artwork again (via 'Add Artwork') and save - the artwork is STILL wrong.

I have deleted the track in iTunes, gone to the original .mp3 and deleted ALL data, copied the track back to iTunes, added the correct artwork and saved yet it is still showing the incorrect artwork.

There are 2 more tracks (so 3 in total) out of 27 in the album that are incorrect and I CANNOT change. The other 24 are totally fine.

I'm guessing that there is something in the track's hidden metadata which is wrong and forcing the incorrect artwork - no matter what I do.

What is going on and how do I correct this?

iTunes is running on a Windows 10 Pro desktop pc and the iTunes version is 12.13.7.1

Thanks