Hello,
I had the EXACT same issue happen to me and I FOUND A SIMPLE SOLUTION tonight that worked for me! This solution can be used on an Iphone. I know some of you use Macbooks to organize your music, so if you'd like me to help you with a Macbook issue, leave me a comment/message.
Over the years I've purchased thousands of songs using the same apple ID and password. A few years back I purchased songs on the library on my Macbook, but recently I've been purchasing all my music on my iphone.
Over time I noticed some of my songs were missing from my itunes library. At first I was just annoyed and confused, so I'd end up re purchasing the songs. A week ago I purchased the Iphone 6 plus. I discovered that even after I downloaded all my music from Icloud, many albums were missing. I was very annoyed because I felt that apple shouldn't be making these mistakes, especially after we pay so much for apple products. Many of my family members and friends told me they experienced the exact same problem. I was upset and thought my music was lost, until I started messing around with my Iphone tonight.
I don't work for apple- I'm just a semi tech savvy college student. I will try to explain this the best that I can.
Try these steps on your Iphone.
1. pick up your iphone
2. click on the "Itunes Store" icon, and sign into your apple account on itunes
3. navigate back to your home screen
4. click on the "Music" icon
5. click on the "more" Icon (should be on the very bottom of screen, to the right of the "songs" icon)
6. five options should appear. The last option will have a little house Icon and have the word "shared" printed next to it.
7. click on the "shared" icon
Although I've always used the same apple account to purchase all my music, for some reason their were two apple libraries in the "shared" folder.
The first option under the shared folder said "Blakely's Iphone" and the other option said "Blakely Jones Library" I clicked back and forth between the two libraries and I found that all the albums I thought were lost before were actually in the second library, along with songs I'd purchased way back in middle school!
If you are lucky, there will be two different libraries in your shared folder, which simply means your songs were divided into two libraries. I have no idea how this happened. For some albums, half of the albums songs are in one library and half are in the other library. I believe this is a mistake on the part of apple. Not everyone has the time to mess around with their phones and recover their missing music, so apple really needs to solve this. However, I'm just really happy I found where my songs were hiding!
My next question is, how can I combine these two libraries on my phone so that I don't have to constantly switch back and forth between them? I will bring my iphone in to an apple store tomorrow and ask them to help me combine the two libraries on my phone. I'll post an update once I get an answer! I really hope this information has helped you! I'm unsure if this method will work for everyone, but you should try it just incase! There could be so many other issues going on with your itunes account, but this is the method that worked for me. Good luck!