Yesterday, after I was finally convinced that I'd conquered all the data-hell challenges I've faced in Joplinland over the past 6 weeks, I was working in Joplin desktop, editing a note. Sync was running. Suddenly an entire notebook with >200 notes literally disappeared. Poof. The sync completed and all of my tags disappeared too. All tags associated with my 4,000 notes are gone. WWHHHAAAATTTT??
I have no idea what happened and, frankly, I'm too exhausted to find out. So this is an informational post. I'm not asking for any further assistance, as I've been taking more than my share of help from the generous souls on the Board. I can fix this by reloading backups. But it shouldn't happen and it's frustrating that it does.
At a low level, when it synchronises with Dropbox, the app gets a list of all the latest actions on Dropbox. This might be update, create, delete. In this case there was one or more delete operations (maybe just one on a notebook, or multiple on notes) and the app applied this locally.
Without any knowledge of what happens in the Dropbox folder we indeed cannot help. The thing is that Dropbox is also synchronised to the filesystem somewhere and if something's deleted there, it will be deleted on the Dropbox server, and in turn in Joplin. In fact this is why we don't recommend anymore to use Dropbox or OneDrive, it's too much of a mess to figure out what happens when there's a problem.
Joplin Cloud is mostly immune to this because users cannot do much with the sync service other than sync their notes.
What we'll do in a future version however is provide a detailed log of delete operations and why they happened, which should help diagnose issues like this.
I don't use this Dropbox for anything except storing my Joplin installation. It contains no files, other than what Joplin added. I did that intentionally to try and avoid the kinds of issues I've been running into. I'd be happy to use the Joplin Cloud as an alternative, although now I'm worried about trying to successfully migrate my multi-device Joplin installation there. Regardless, I first need to fix what I've got.
Thanks again. And, by the way, thank you for all of your hard work on Joplin. Through all my issue and bitchin', I probably sometimes forget to properly express gratitude for the thousands of hours of work that you (and other developers) have done in sharing this with all of us.