Q: WARNING: iCloud Music Library just destroyed my Mac's iTunes Library

once you have followed those steps, upon reopening your lovely old iTunes library, iCloud Library will already be off. It will prompt for you to turn it on. Deny the prompt.

interestingly it didn't ask me to enable...however if you go to preferences there is a toggle button for iCloud library, which I've set to off until this is fixed.

This is a worry, I updated to 12.2 earlier this morning. I got no prompt either for toggling it on. Already had match running. My library appeared to look ok but I need to inspect closer after seeing this nightmare scenario. I wonder how many have been hit. Apple, can you do nothing right?

Something similar happened to me... I turned on iCloud music library on my iPhone and noticed that it screwed most of my album art, didn't check the tags but this morning one of the songs was wrong, I hope it was also before I disabled Apple Music and all album art got lost, then i synced my phone with my macbook pro and every album now has its old correct art. I don't remember if I had already updated iTunes at the time. I think if you disable Apple Music on the iPhone it will be disabled on the Mac too, am I right?

I am experiencing the same problem. The complete music library is messed up right now. Replacing the .ITL file will only let it look okay but it clearly isn't. The files itself are damaged because these show the wrong cover art etc when you navigate to these in Finder. I think the best solution is to restore shut down iTunes, replace the messed up music folder with the music folder from a back-up, then replace the .itl file and then restart iTunes. Haven't tested it by myself yet because I don't have my back-up around here but in like 5 hours I can tell if it works. I'm glad it didn't mess up my movie and tv shows...

Same problem here. I sent Apple a support email about it before finding this thread. Hopefully it'll get their attention. Insane how huge of a mess this is.

Seriously?!!!!!! I'm relieved that the iOS match problem is now sorted but now I'm actually scared to lift the lid on my Mac after reading this lot. Shall I leave it alone for a while until Apple sort it out. I mean what will happen. Will my iTunes library go tits up and then match it to all my devices. Sheeet!!!! What's the latest anyone been I touch with Apple?

I suggest you wait and see, and keep a time machine copy of your library at hand. As long as you disable iCloud Music Library you can still use Apple Music streaming, but you won't be able to add Apple Music files to your library (maybe you can download them though, didn't check).

This feature was intended to allow the merge of Apple Music and local Music Library but it's done with the attitude that "iTunes knows best" so Apple instead of just adding your Apple Music tags to the local library is adding all your local library tags to its cloud, but since "iTunes knows best" they are also changing all your tags in the process. This is crazy

Same issue here. It was easy to recover my library but turning off iCloud Music Library is hardly an ideal long term solution. I'm currently deleting everything from my iCloud Library from another Mac (Hoping that starting over might solve the issue). This is cloud services at their worst. Utterly opaque to the user, no easy way to reset or start over, and the damage caused propogates across devices.

I too used to have an iTunes Match subscription.

Can you delete songs from your iCloud library? I thought once you disable it from iPhone it wipes out his library...

I'm basically doing this:

http://www.wired.co.uk/news/archive/2012-01/12/how-to-reset-itunes-match

I wouldn't recommend it (might not even work. I got about half way through deleting songs and now it can't connect) but I'd rather have an empty iCloud library than a destroyed one

Do we know if this issue is specific to Mac or Windows iTunes - or does it not matter. Only reason I ask is my library seemed ok earlier but I didn't inspect it in detail. I also don't want apple music (as I prefer to own a song) so this is not enabled on my machine. I wonder if signing up for apple music is triggering this.

I don't know if this works even if I don't have iTunes Match. Sure it looks a lot of trouble for just removing tag data from a server :/

When you sign up for Apple Music iCloud Library is not turned on by default. You can happily stream from Apple Music without the iCloud Library, but you won't be able to add songs entries to your local library (which was one of the selling points of Apple Music for me ) All these issues are related to the way iCloud music Library matches your local library with Apple Music tags, so for example if you have the EU version of an album and Aplpe Music only has the USA one you'll get it changed. It would've been nice to have a disclaimer of what iCloud Music Library did when asked wether I wanted to turn it on :/

Also upgrade iTunes and phone for Apple Music. Clicked box for "iCloud Music Library". As I understood it, Apple would check our music, and if it found the same track in their database, it would add that to your "cloud library". Tracks that weren't in Apple's collection/database would have to be uploaded. I have a lot of out of print classical and soundtrack CDs that I've ripped, so I figured that those would have to be uploaded. A process that would be slllooowww and take days, since I also have about 20,000 tracks in total.
When I checked on the phone, artwork was messed up in places with no patterns that I could figure. Usually, Apple would take a composer's name and slap some art that wasn't the actual LP/CD. So, I'd get John Williams' Star Wars or Schindler's List with new art from some misc album that has that theme on it. Or a Mozart or Beethoven symphony with some random art from a recording of the same symphony. Uh... no thanks.
I figured it might be temporary as everything gets uploaded... then I clicked on some tracks, and not only was the art wrong, the music was wrong. oh, it was the same composer, but the wrong music.
It's just frustrating.
Luckily, all the music and info on my iMac/external drive seemed ok.

Here's my solution. Since I have so much music, I already have a large capacity iPod with all the music on it. So, I'll keep carrying that. It's never bothered me before, so...
and I'll turn off "iCloud Music Library" sharing on the Mac. I won't have access to all my out of print music on the phone while I'm on the go,  but that's ok. That's why I have an iPod. Trying for  a more complete collection, can go into Apple Music and manually "add" albums that I already own to my list.
Just using Apple Music and Spotify to try things I don't already own anyway... If I find something I really like, maybe I'll buy a hard copy, and put that on my iPod that doesn't/won't sync to the cloud.