Consider post #3280724. Full image URL at https://danbooru.donmai.us/data/__hatsune_miku_vocaloid_drawn_by_pupupu_1053378452__b1cdefef75e0a417f82e9302bdb048b8.jpg loads fine, but https://danbooru.donmai.us/data/b1cdefef75e0a417f82e9302bdb048b8.jpg returns 404. This appears to apply to around half of images surveyed. This happened yesterday as well, but not two days ago.
Edit: this post got fixed by itself literally two minutes after I submitted this, but it's still occuring on other posts. What's going on with this?