Editing Tags with iTunes 12.6

This issue is not new. iTunes tagging has always been maddeningly capricious, and often downright bizarre in its behavior. I use the "MusicBrainz Picard" app, which is great for comprehensive tagging and sorting, with only a moderate learning curve.

Do you have Apple Music? New version spent a long time analyzing my library and uploading hereforto non-uploadable files (ALAC 24 24x96 files, old AAC files that had chapter markers in them, etc). It is GREAT because pretty much EVERY file that failed to upload is now in the cloud. HOWEVER - while this is going on, often tag changes you make do not hold, as it overwrites the changes with what it pulls from the cloud. Have you tried changing the tags when there is no Apple Music spinner in the upper right of your iTunes window?

In followup, no the chapter marked AAC did not upload. The 24x96 did. I saw the same weirdness you've seen, if you have Apple Music the indicator is not always visible while they sync, and the cloud version can often overwrite the info of the local version. I find the amount of time you have to edit was when you add music is almost 0, so either tag BEFORE you add to iTunes, or wait for iTunes to sync to Apple Music, then wait a little more 😉, and THEN you can change tags and it will hold....

For me, since I am doing a whole bunch of other stuff with my music (amateur audio taper) I use xACT to tag it before I add it to iTunes. It still does not have ALL the fields, but the most important ones. Then I add to iTunes and wait a bit before I edit.