Purchased Music Missing From iTunes/iPhone

I've noticed several songs that I know I've purchased are totally missing from my library. I found 2 that I know I bought when they came out a few years ago were not on my phone. Not only that, they weren't in iTunes, my computer, and they didn't show up in my purchased history in the iTunes Store. They aren't on my Mac either. I've never deleted them.

I've had to re-purchase a handful of them but I don't want to keep doing this. Over the last few weeks I've found several songs that I've had before not show up for me. Is there a solution for this? It's frustrating to lose stuff you've already bought.