Dears,
I have a persistent issue in syncing notes via desktop Joplin client to my backend NC. Joplin on my mobile device sync is fine but the issue is with the desktop client. I think this is causing discrepancy between notes on mobile and desktop.
Desktop Joplin client version : 2.7.15
Host Operating System : Windows 10 Home 21H1
Mobile Joplin version : 12.7.1
Host Operating System : iOS 15.2
Backend : NextCloud
Sync Target : WebDAV
Joplin interface pane showing the error:
Log files would help a lot here - How to enable debugging | Joplin
Out of interest is there a reason why you are using the WebDAV target rather than the NextCloud target as you are already using NextCloud?
Thanks Daeraxa for your response. The debugging log is following 
for review.
sync-sqlite-constraint-not-null-errors.log (59.6 KB)
Regarding the WebDAV target, no specific reason for selecting it. Shall NextCloud target be better ?? I changed it now as of writing this post and made a sync, then the same error shows again 
I'm not 100% sure if it actually matters tbh, just something I noticed.
As for the log, I'm no expert on the matter so happy to concede to authority but it looks like its some kind of bad data in your system?
If you open up your nextcloud and look for this file - c94da607d70c46eab0fe8e477b1aaeee.md can you post its contents (or if sensitive see if anything look obviously wrong with it?)
Today the desktop client succeeded to sync !
I will be leaving the sync target to be NextCloud from now on and ditch WebDAV.
Question : Shall selecting a different sync target of the mobile Joplin , than the desktop client, say WebDAV for the mobile and NextCloud for the desktop, cause any issue ?
Question : In the same vein, and regarding "Note History" setting, shall setting two different note history saving days between mobile and desktop cause any future issue ?
Word of warning, changing the sync target isn't a trivial change and you could lose all your data if you aren't very careful. You should follow this guide if you do plan to move.
Please just make sure you take backups before you do anything at all, I recommend installing the simple backup plugin as that will backup both your profile settings as well as performing the JEX export for you.
Honestly not sure, I don't know what the functional difference between the two sync targets actually is I'm afraid.
The lower of the two settings is what counts. Essentially neither client knows the other is connected so when it deletes the data based on the revision setting it does so locally then just syncs that deletion to the target.
I still wonder why this error happened. It would have been good to see the file c94da607d70c46eab0fe8e477b1aaeee.md in case it's something we need to fix.
Since this provoked your interest 
I see nothing problematic in the note.
c94da607d70c46eab0fe8e477b1aaeee.md (650 Bytes)
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