It happened to me too just this March 22 and I was able to restore about 95% of my notes.
I contacted apple support and they assisted me by screen sharing until we were able to restore them.
They will help you look for a back up in your iPad (not in the icloud) and they will help you restore that. Hopefully you do have back up in your iPad. Lucky for me cause my iPad was programmed to have a scheduled back up.
Reach out to them via: chatsupport.apple.com
They will initially do a basic troubleshooting and when they cannot go further due to technicalities, they will have someone call you.
I hope you recover yours.