My main issue with this entire problem for me was Apple dumping remixes of original songs that it couldn't find on iTunes or keeping the metadata fro the remix and pasting over that with the original track .mp3 off iTunes which was soul-destroying because it takes me ages to perfect my library and find awesome remixes and songs that not everyone knows about. So I was annoyed because I wanted Apple Music to work seamlessly since I am slowly building an entire Apple eco system. So the goal was getting those remixes onto iCloud Music Library without Apple wiping them over.
I found what helps is definitely the .itl trick and backing up your music folder once that .itl trick is done. I archived mine into a .zip folder and tucked it away safe for protection. Then turning off Apple Music and iCloud Music off on all devices, Mac included. Wiping all music of iOS devices. I know, big step. But then re syncing the music onto iOS devices without Apple Music hanging around. Now your iOS devices should have your original music, pre-8.4/apple music update screwup. When that is done, turn on Apple Music and iCloud music library back on on your mac or PC. Letting that sort out and all. Then when thats settled, with resynced music on iPhone for example; go into settings and turn Apple Music and iCloud Music Library back on. When the dialog for iCloud pops up, CLICK ON MERGE. MERGE MERGE MERGE.
This will scoop everything up together regardless of whether songs are on iTunes or not. Check to see if songs are good to go with right remixes/artwork etc. If okay then repeat on other devices.
It worked for me, it should work for other people.
Steps (Organised view 😝)
1. Do the .itl backup trick first on mac / pc and that should sort out
2. turn off apple music/icloud library on all devices including mac.
3. wipe music off ios devices via Settings-usage-music-edit and then delete. All devices!
4. Re sync freshly musically emptied devices with computer again with out apple music hanging around.
5. Turn on apple music and icloud library on again on mac/pc and let that sort.
6. Go to ios devices and turn on apple music and icloud music library in settings on ios devices
7. CLICK MERGE! MERGE MERGE MERGE.
8. should be good to go, go to music app, click my library, let it load the library. Should be okay. Just have a scroll through to see if things are okay.
Personally I think Apple would have avoided these problems with metadata and wiping away remixes that aren't on iTunes and all these other troubles with the launch if they brought out iTunes 12.2 before they brought out iOS 8.4. Thinking about it in regards to the steps above if we all set up apple music and icloud library from computer rather than mobile devices it wouldn't have turned bad. I think. Thats my personal opinion. If im right let me know.
Hopefully ive been a help.