I also had this problem on my iPad 2 and got so crazy. A lot of notes disappeared leaving me with only 3.
However, my iPad2 was stolen, then I got iPad4. Surprisingly, when I checked the note app, I found my 3 notes left on my previous iPad2. My new note on the iPad4 also disappeared.
But this is what I just found out -
- Log in to your email from your browser (the email you configured with your iPad)
- when you can view your emails, click the TOP LEFT CORNER icon (that has 3 lines)
- A sub - menu will come out
- Scroll down, you will see NOTES on the menu
- Click the notes, and you will find ALL your notes there.
NB- I don't know why apple can't solve this problem but there is another option.
Download another Note app from App Store, use it and you will be ok.
Hope this helps.