I've been trying so many things for so long to get this to fix. I tried one thing last night, and it worked perfectly. At the very least, for one playlist.
I had been using the same music folder for Itunes to draw all of my music from, divided into artists and what not. Last night, I had read on other forums of dragging music to my desktop, and having itunes grab it from there. I didn't want to keep moving my songs around, so I moved it from the original folder I had it stored in, and put it in my "Itunes" folder under music. It fixed it. I think it might have to do with the location of the folder, and it is just not grabbing the information correctly.
I first exported the playlists I wanted, so I didn't have to hunt the music down again later. (File>Library>Export>Playlist while you're in the playlist you want to export)
Then, I got the album/artist's music that wasn't working correctly on my Iphone in the search bar on Itunes. Once I pulled the music up, I deleted all of the artist's music, or the album that wasn't functioning correctly.
I then cut the folder the song was in (Luckily I had the songs in folders, or this would be really tedious), and pasted it into my Itunes/media/music folder, and then re-added all of the folders I had just moved. (in this case, I moved four folders simultaneously.)
I imported my playlist again (File>Library>import>Playlist), and the music worked perfectly.
I don't post on forums often, if even at all, but I think since so many people had this issue, I REALLY hope this helps even one person out.