Reset purchased tracks' metadata

Sadly this issue of purchases reverting to the original iTunes Store metadata seems to be a bit random and unpredictable. I don't know of any way to force it to occur. Hiding purchases that do get affected is the way to preserve your custom changes, but it sounds like it might be too late for that news to help you.

See ExportImport for a script that could potentially export your custom details from a backup of the .itl file and then apply them to your current library.

tt2

Then I don't think there is any quick fix for you. The only thing that might help is to use the column browser with artists and albums enabled. Step through the artists in sequence spotting and fixing any anomalies such as split albums as you go, and keeping a note of where you got up to when you done enough housekeeping for one day. Backup the library occasionally.

tt2

To stand the best chance of the script being useful you would need access to an .itl file in the Previous iTunes Libraries folder that predates your subscription to Apple Music. You'd also need to temporarily rename the iTunes Media folder during the export phase so that current details embedded in the tags cannot be read and iTunes can only read from the old database. You should then be able to generate a export file that hold your custom details, and import those back into the current library. You may need to change which details are included in the export phase to ensure you only capture the details that you've noticed iTunes has "corrected" for you.

tt2

Apologies for the late reply.

You can copy the current .itl file to a separate file at any point, however if you are signed into your Apple ID then there is always a chance that store metadata can overwrite local metadata for items that you've customised, and if you have an active iCloud Music Library with Apple Music or iTunes Match any data there takes precedence and. merges into whatever is stored locally. Hiding purchases is the only way I know to avoid unexpected changes, and make sure that you see the same details across multiple devices.

tt2