What is the iCloud Music Library?
The iCloud Music Library is a service that Apple provides which allows you to store your entire music library (up to 100,000 songs) on the cloud for access across multiple devices, what happens when you send your iTunes library to iCloud is it scans the metadata information and also uses audio fingerprinting to find the best (most accurate) copy of the same file on Apple servers (this is actually really beneficial if your library is full of low-quality audio files as they're replaced with 256kbps AAC files of the same song) and replaces the existing file (the next time it is downloaded from the cloud) on your computer with the copy of the file from Apple servers.
This means that your cue points, flips, beat grid info, saved loops and just about all other tags will be gone from the files you had previously imported into, or downloaded from iTunes.
If you would like to try out the iCloud Music Library, we advise that you make a backup of your iTunes library first so if anything goes pear shaped, you can recover your library and continue DJing.
If you do not have a backup of your iTunes library from before this happened, you'll need to reset your tags as there is no way to recover this information.
We strongly advise against using iCloud Music Library or iTunes match for your DJing library.
How to disable the iCloud Music Library
To disable the iCloud Music Library you will need to go to the preferences window for iTunes, and disable iCloud Music Library under general preferences.