I've just made an account now to ask for help on this issue, so I apologise if this is in the incorrect category or anything.

My computer crashes pretty frequently while using Krita. Now, rather than being the sort to forget to save, I like to save a lot. Here's where the problem comes in; recently, my computer has been crashing while files are in the middle of saving, and when I return to the file, I'm told that it's not a valid Krita file. I've been trying to make it a habit to save backups of art, but typically, it never crashes when I've made backups, so I forget to make one next time, and then it'll crash.

So, I'd just like to know, is there any way to recover these files? I've seen ZIP file repair tools recommended, but I'm not certain if I need a certain one that would be able to read .kra files, as one that I've tried using didn't seem to do anything in the slightest, and the files are still invalid.

Trying to extract files using 7zip, it works on other Krita files, but the invalid ones give me a message saying that they cannot be opened as archives.
Attempting to fix with Winrar's repair tool, I'm given the reason "Invalid document: no file 'maindoc.xml'." - not to mention the file size is miniscule in comparison to the proper file size, so I get the feeling that there's a few too many files missing. The more methods I try that are currently at my disposal, the less hopeful I get that I might be able to recover it.

... Autosave isn't working for you? Because we have autosave active by default. There's also incremental-backup actions that can be hotkeyed and will save your file with a incremental number.

We made a fix recently that should make saving a little more robust.

But I am afraid there's no data whatsoever in those corrupted files. Krita files are zips, so if you cannot unzip them, then there's something seriously wrong. :/