I updated my Early 2012 MacBook Pro to macOS Sierra today. I cannot get iTunes to work. It just constantly pops up a little window saying "Writing ID3 tags...". I cannot even leave it open in the background because it is slowing down everything each time the window pops up. Even weirder from what I can see in the album view that is is stuck on, it has changed the artwork on some of my music. I am assuming this is related to the Sierra, but I hate to rollback my MacBook just to get iTunes to work.