There are terrible problems with the automatic saving feature, if you rely on it I strongly advise you to make a copy of your “backup” folder and session.xml in %APPPATH%\Notepad++ before every closing of either Notepad++ individually or the entire computer, and keep several copies of them.
It’s better to copy also the N++RECOV folder if you have one, although I’m not seeing problems with that lately.
For me it’s not an unbearable problem because I always use the Windows’s hibernation, so I restart Notepad++ only once every couple weeks.
Recently I haven’t experienced problems when closing explicitly Notepad++, but every time that I let it be closed by the Windows’s shutdown procedure I lose all the contents of the backup folder, and thus all the so-to-say unsaved files if I’m not careful.
What usually (maybe always) happens is that the “backup” folder gets nuked, and after that at the first next start of Notepad++ the session.xml gets cleaned of all the now unreachable unsaved files, without any warning.
At that point you’ll better have a backup of session.xml besides the backup folder, because although all the files’ contents are in the folder there are easily old leftover files in there too and it will be hard to find out what you were working with if you don’t have the session.xml references.
As I’m at it, beware that there are frequently problems after a system crash or especially a Notepad++ one: it has a feature that supposedly attempts to save your work, but it actually often (every time in the last couple years, to me) does the exact opposite by zapping the entire backup folder!!!
So as soon as you see a message from Notepad++ that it is about to crash before clicking the message go to %APPPATH%\Notepad++ and copy your backup folder and session.xml, preferably once after every Notepad++ message (I don’t recall well but there are two or three, and I seem to recall that the latest state gets attempted to be saved only after the first).
BTW yes, it is an horrific problem, it even got me to learn vim in search of a more reliable alternative, but it turned out that even vim is not really as great as they say so I’m still using NPP.
After the next loss I’ll spend some months learning emacs, then probably something else and in a couple years maybe I’ll have freed myself from this editor.