open settings / icloud / make sure notes has the green slide arrow turned on.
If it is not there & turned on, you must scroll to the bottom & sign out. (it’ll say all is lost but they
do show back). A new notes must be created in icloud & when u see merge, do it. Now sign back
in using your apple login id.
also you can try other icloud notes apps, for example: https://itunes.apple.com/us/app/id1140487495