The covers from Amazon are in fact always fucked up, but that's because Amazon is awful and there's only so much they can do within Amazon's rules. There's an option to turn off all Amazon covers, and then you can go in and manually choose a cover from the user-uploaded ones. (You can also use that dialog to steal the Amazon-provided cover and pretends it's a user upload, not that I would ever suggest breaking Amazon's TOS that way.) It's a little more trouble, but Amazon will no longer have the ability to random change what cover displays on your book.

(There's also a widget you can put on your front page that shows you a rotating selection of new user-uploaded covers for Amazon-covered books you own, if you just want a fun way to waste time.)

Do you mean you have books you added to your catalog that aren't appearing it in anymore, or---? There was a data loss issue late last year, iirc, but they managed to retrieve all the books from it, although some of them might have weird metadata or be in the wrong collection. Or you might just have books that accidentally weren't added to your default collection - I've panicked about that a few times.

IF you really have lost books in your catalog, if you report it on the "bug collectors" talk group, they're usually pretty diligent about tracking down and fixing those types of bugs; ongoing book loss isn't something I've seen anyone else report lately.