Can't put music on my 4th generation iPod

I recently got a refurbished 4th generation iPod touch, 32 GB, and am trying to put music onto it, but not all of the songs will load. It's not a capacity issue by any means, not even half the space is being used. All of the songs appear in the playlists but some are grayed out. I took everything off and tried loading just the songs that wouldn't load, and still no dice. Most of the same files went onto an older iPod a few years ago, is there a setting I'm missing?