The version: Joplin 1.4.19
I've lost about nearest 6 months of notes, not sure about previous ones.
It was caused by a series of my own stupid operations: change target directory to use Dropbox client to speed up sync, not watching sync and find all notes in "Conflicts", try to sort out conflicts, and finally sort notes by created&updated, found out the loss.
Luckily all e2ee encrypted data had successfully synced with Dropbox this morning, when everything is fine.
I tried delete ~/.config/joplin-desktop, re-link Dropbox, but this time the Joplin-Desktop is using directory App/Joplin(1), not Joplin where data were located