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Meshes don't show without a texture present, so you're most likely missing the mesh, but it's impossible to tell which one based on the picture. There are a few times where you could be missing other files, but usually if it's an elder hair or clothes.
Check the tooltip (the hovertext when you mouse over the thumbnail) to see if it says anything.
If there isn't any hovertext, you can try to package a sim with the hair in Bodyshop, and see if it picks up the file. Just make sure to delete the sim from the sim bin after, as sims with missing hair meshes will usually be quite buggy in Bodyshop.