I upgraded to Mac OS 10.12 GM and many of my albums in iTunes are now missing album artwork (where they weren't before the upgrade). I tried to use iTunes to add the missing artwork, which appeared to fix it, but as soon as I sync my iPhone, the album artwork disappears from iTunes on my Mac, and it's also missing from the music on my iPhone.
I've reported the bug to Apple and duplicated it on Open Radar.
