Repair security permissions for iTunes for Mac
Occasionally incorrect security permissions may prevent iTunes or Music from operating normally. To make sure that your profile has full read and write permissions to the iTunes folder and all its subfolders use Get Info on the iTunes folder in Finder. (In Catalina or later go to ~Music/Music instead.) Click the lock at the bottom right to make changes. Make sure that Locked isn't ticked and that your own account has Read & Write access, then use the gear icon at the bottom to Apply to enclosed items and confirm. Repeat with the media folder if it isn't a subfolder of the main library folder.
Multiple tags (MP3 files only)
If you have applied the permissions fix and tracks still won't accept your updates then a remaining possibility for MP3 files is that they have multiple tags. The ID3 specification allows files to have multiple tags in different versions and languages, but iTunes and Music only work properly with single tags. When multiple tags are present the application can sometimes fail to apply updates to the tag that it later reads back (presumably updating one of the others in the file) and it is also possible that iPod & iTunes may have different rules for which tag they give priority to. This could lead to situations in which everything is properly organised in iTunes but then inexplicably falls apart on an iPod or iOS device, or tracks that display different information in Finder or another media player. There are 3rd party tag editors that can manipulate multiple tags but I don't have a recommendation offhand. A workaround in iTunes is to use File > Convert > Convert ID3 Tags... > None a few times to remove all existing tags and then File > Convert > Convert ID3 Tags... > v2.3 to build a fresh tag with the information still held in the database. I've read in the past that iTunes isn't fully compliant with the v2.4 spec. although this may no longer be the case, however support for v2.3 is widespread so I would suggest using v2.3 over v2.4. Any embedded artwork will be removed so this needs to be replaced if wanted. Mac users can try the scripts SaveAlbumArt and RestoreAlbumArt before and after the tag cleaning process respectively to backup and then restore the images.
AirPlay
iTunes, or Music in Catalina or later, might not be able to save changes to tags while AirPlay is active.
WAV Format
iTunes or Music can associate store artwork with tracks in .wav format, but these files don't carry a tag so you cannot add custom artwork. Any metadata associated with the files is only saved in the iTunes database and is lost if such files are imported into a new library.
iTunes Store purchases
In some cases store purchases where you've set custom metadata may revert to the details held by the store. This appears to be an unintended consequence of the way that your purchase history in the cloud is integrated with locally stored media. To prevent this happening you can hide your purchases for affected items while retaining a local copy. Unless you have iCloud Music Library as part of Apple Music or iTunes Match purchases also need to be stored locally in order to make changes to them.
Apple Music
There appears to be an ongoing issue where changes made to a library on a Mac may revert to a previous version of the data as held in iCloud Music Library. It may help to power cycle your router and computer, but this doesn't always help. If you run into this issue please use Feedback - macOS - Apple to report it.
Untagged files
There is an obscure issue where tracks that have no value in the name/title field of their tag may not get moved or renamed when changing data in other fields, even though Keep organized.... is enabled. Update the song name to resolve. It also seems that attempts to add artwork to otherwise untagged files may fail so entering some text information first and applying may help here.
Related support documents and user tips:
- TS1277: iTunes: Missing folder or incorrect permissions may prevent authorization (Document retired, archive version)
- HT203538: Resolve issues caused by changing the permissions of items in your home folder (Document retired, archive version)
- Repair security permissions for iTunes for Windows