Are you using/have you ever used any mods? Reverting old content is a common symptom of outdated mods. (And in the case of hats, very outdated, since there's no good reason to replace the entire hats file...)
If you are, someone will probably move this to Mod Support, and you can start with a
SMAPI log (or just remove your mods to see if it comes back), unless you overwrote XNB files, in which case 1. don't do that and 2.
reset your content files :)
If you're not and have never used any mods, I'd still start with
verifying your content files.