iTunes 12 artwork not working

WAV files do not support embedded artwork (or any other metadata), so the only way to associated album artwork with such files is to use the Get Artwork function which downloads images separately - they're stored in the Album Artwork folders rather than being embedded in media files. As you've noted, there seems to be an issue with the methods that iTunes uses to retrieve Store images - the timing suggests that this is one of several issued associated with the transition to the Apple Music service. Hopefully Apple are aware of this and functionality should be restored soon.

Unless you have a specific requirement to use WAV files you'd be better using AIFF or Apple Lossless. Both have identical audio quality to WAV, support embedded metadata and artwork, and - on the case of Apple Lossless - reduce file sizes.

There's two songs that refuse to add the art work for me. They're both MP3s and they obviously have the right album name, etc. I do Get Album Artwork, nothing. I add some from online, nothing. I have no idea what's going on. I have the newest update of iTunes. Windows 10. Nothing's working.

Check that the MP3 files are not set to read-only in Windows and that Windows permissions are not preventing updates to them.

I've looked at all the posts on this across the forum and this is what worked for me - thanks to hhgttg27 for pointing me in the right direction, it did in fact turn out to be e a format compatability problem.. I have Itunes 12 on a Windows 7 platform and have a mix of stuff I bought from Itunes (artwork no problem with download from Store) and other stuff I imported as WAV files. Some non Itune purchased files did actually respond to the "Get Artwork" command but some (even though they were in the Itunes store) did not, and neither could I drag and drop artwork saved as JPEGs on my PC. The solution for these was to click on the album in Itunes so it shows all the songs and then choose "create AAC version". This populates the song list with duplicates of the tracks already there with a new AAC version underneath the existing one - I guess you could leave both in situ although I chose not to do that, but highlighted the old tracks and deleted them to the recycle bin, leaving me with just the newly created AAC tracks. I then chose "get info" from the dropdown menu (clicking on album in Itunes) chose the artwork tab and the "add artwork" button and then double clicked on the target JPEG and lo and behold!, artwork that was previously unresponsive migrated no problem.