This has happened to me twice now. If I am killed in survival mode, any enchanted items I was carrying disappear. All other items drop as usual and can be picked back up, but anything with an enchantment is gone. And no, they do not have the curse of vanishing or whatever. I'm going to give up enchanting things. What is the point of fishing for hours to get mending on a sword that will just disappear the first time I die?