Very complicated issue with greyed-out songs

[Haileybird81]

Yes, this is long. Yes, there's a TL;DR.

So I was trying to add a few new local files to my library today. I followed the standard procedure of "Add them to a playlist and download the playlist on the phone." All of the new tracks are greyed-out and unavailable.

Attempting to fix the problem myself, I reinstalled the app on my phone, thinking that I could just try downloading all the tracks again, allong with the rest of my library (Let's not discuss my thought process for that...clearly not my best idea!)

The vast majority of my local files are greyed out now, including many that were working perfectly fine before I reinstalled. There are even a few instances where only a few tracks from an album are greyed-out. All of my local files are on two playlists each, and all of those playlist have been downloaded to my phone. Some tracks are available on both playlists, some appear on one but not the other, and the rest are unavailable everywhere. 

But wait, there's more! Some songs that I've saved to my library (not local files, and not on playlists) are greyed-out now too. (One such song is a long-time favourite, See You Again by Wiz Khalifa feat. Charlie Puth, a devastating loss for my eardrums.) This part also gets more complicated: some tracks on an album are greyed-out if I get to them from Songs, but available if I access the album through Recently Played. (The album is Handwritten by Shawn Mendes. I listened to the entire thing just last night, and now only four songs are available.)

I'm a premium subscriber with an iPhone 6 currently running iOS 10.3.3 if that means anything. I will be updating to iOS 11.0.1 now, will update if anything changes.

TL;DR - Newly added local files were greyed-out. Reinstalled app to try again. Everything went haywire. Help!