I am having a similar issue after updating all my devices to iOS 17.1.1 Notes just immediately disappeared. The disappearances seem random and like the poster above are "simply gone" not deleted just evaporated across all my devices and icloud for both shared and unshared notes. Its very random and very hard to detect as it's a small number of notes. There seems to be no common thread to their character. Some had video attachments embedded, others images, while others were pure text with no special formatting or features whatsoever. This is very disconcerting as most users probably won't even detect they are missing notes (until they need them) unless like me they rely on them to stay organized. I may have to do some serious thinking about using them this way as this is the third time I have been snake bit by imponderable disappearance of notes. What's that only saying, "fool me once shame on you; fool me twice shame on me"...fool me three times...well now I just look silly. LOL