In case anyone else is looking at this like I was a moment ago...
Sync issue between Mac, iPad, iPhone, iCloud. If I enter or edit a note on web based iCloud notes, it would appear on all devices. If I enter a note or edit on the Mac it will sync across all devices. If I edit or create a note on either the iPad or the iPhone it will NOT sync across any devices.
This is maddening because you see a note from the Mac on the phone, assume it is all syncing fine, edit it on the iPhone/iPad and the edits do not show next time you need them on the Mac, but are there on the phone. If you use the notes app across devices for work as I do this is a big problem.
Various reports of a January iOS update that fixed the problem, but as its now August and I still very much had this problem its a different issue. The solution I found was to log out of iCloud on the iPad and on the iPhone and log back in. Normal syncing across devices resumed. I lost the out of sync notes on the devices though as they were reporting they were iCloud notes and not local notes, so when logging out of iCloud they went with it, even though they were never actually on the cloud, so make sure to manually copy the out of sync notes from your non-syncing devices BEFORE logging out of iCloud if you want to keep them!
I think the problem may have been that I was logged in to iCloud with one email address and the Apple Store with another email address. That should not have affected notes syncing across iCloud, but is the only obvious thing I can see it could have been. I have now logged in with the same iCloud address on the store too and it all working. May be worth considering trying that if you still struggle after logging out.
Cheers.