Shrunken pick guard syndrome, several manufacturers glued pickguards directly onto the wood. The pickguard would shrink and crack the top. Here's one being repaired. The guard has been removed and the cracks are being glued up supported on the bottom with small spruce cleats. I like to make mine round, it allows me to use a plug cutter and then I can thin them down to whatever thickness I want. In this case I shaped them to fit around the braces.