Why were my song ratings erased and playlists emptied on iTunes?

I'm looking for a possible explanation as to why this particular thing happened so it doesn't happen again in the future. I tried to cover every detail I thought was appropriate in case someone can point out exactly what went wrong.

First of all, I have a modest library of 3500 songs on my iTunes that I keep pretty organised with playlists and star ratings, and I try to store all of my data locally (ie. not on the cloud). I synch my whole library to my iPhone, so basically I try to keep my iTunes library and iPhone music library identical and have all of my music physically downloaded onto my phone (so only music available offline). I don't use iCloud Music Library and keep it off.

I do use Apple Music on my phone, however, to discover new music. I had it on automatic renewal for a couple of months but let my subscription lapse a maybe a over a week ago - ergo, I didn't have Apple Music for several days.

I decided to subscribe again a few days ago and all was good. I hadn't synced my phone since my subscription lapsed because I hadn't added any music, until yesterday when I bought a few singles on iTunes that I wanted to sync to my phone. However, they wouldn't sync to my phone after 2 or 3 tries, so I looked around my phone settings and noticed that iCloud Music Library was turned on. I'm pretty sure when I re-subscribed to Apple Music, it turned iCloud Music Library on somehow.

So I turned iCloud Music Library off, and then I tried to sync again. Only this time, a majority of my purchased music weren't syncing to my phone. All of my other music synced through. The only way to access my purchased music on my phone was to "show all music" and, I suppose stream them to my phone. Some of them would stream and I had the option to "download to phone" but most of them wouldn't even do either, they would just appear in my phone library but unable to play. Still the same after syncing 2 more times.

I deleted all the music on my phone through my phone settings then synced with the option of not syncing any music on iTunes, and for some reason it still synced one purchased song. I deleted that one song manually, changed to "sync all music" on iTunes to re-transfer my whole library to my phone, but it still refused to transfer pretty much all of my purchased music. And on top of that, I noticed all but 40 out of 3500~ songs had their star ratings erased on iTunes after the sync finished.

One last shot to try and get my music on to my phone, I deleted all the music again, backed my phone up, resetted it completely, restored it from the backup and finally synced everything.

Finally, I clicked on one of my playlists and noticed that it was empty. I checked the rest and all of my manual playlists were empty. The only ones filled were my smart playlists relying on date added and play counts.

Basically the whole structure of my entire library was ruined. I have no idea why or how any of this happened but I'm quite sure iCloud Music Library was the beginning of it. I tried restoring from temp files to no avail, nor did any saved previous itunes library files help. I have a full iTunes backup from September 2015 that has everything up till that month preserved, but I ripped a lot of albums during Christmas and I don't want to lose the date added / play count metadata. I temporarily restored the September 2015 library and screenshotted as much as I could, so I'm just gonna have to manually recreate the playlists and enter in the ratings again.