I am sorry but there is no info about how a folder disappeared.
I tried rebuilding the folders from scratch several times in different user accounts using a back up.
But the same thing happens,
There must something in the folder causing a BUG with iCloud ( i know hi word is not allowed here) but it is what it is
Here is what i did
1 I backed up the notes folder which is "group.com.apple.notes"
2 Started fresh off-line using th preference "on my mac" as default
3 Dragged "group.com.apple.notes" into the directory and tarted notes, worked perfect.
4 But as soon as i dragged, copied, moved anything to iCloud directory, the same folder disappeared!
So i then decided to try the same thing with a new Mac user!
1 Then added it to a new MAC user and imported dragged the folder "group.com.apple.notes" to that user from a ext HD
2 Worked flawlessly, left it syncing for a day, check the folders over the net via safari iCloud website well
3 Then the next day i added a few things to the previous disappearing folder, within hours it again disappeared!
I am talking about a ew mac user!
The folder contains thousands of notes divided in several sub folders, attachments like photos, videos and web links,
But there are allot less its in this disappearing folder ten a few other folders which have no issues syncing across all devices.
So i can't figure out what th problem is, but its either some attachment or link inside a note or iCloud itself because iCloud can not play videos i add to notes, they appear as if plugins are missing, yet on the iPad once the notes are synced i can play the videos flawlessly creating a whole reference subjects., great when it works but it the folder disappears!