Hi
I started to write a tool to try to fix broken .kra files (as a functionality of Buli Commander plugin)
I’m far from something that could be provided in plugin (I’m trying to find time to draw, I took time to write other plugin too, and many other things to manage in my life…) but if you can provide a link to broken .kra file, I’m interested.
According to what is corrupted in file, maybe it can be restored, maybe not.
The reason why a file is suddenly not valid anymore could be:
- A third party software (or a virus) that made something on the file
Extension is not visible on your screenshot, if you can also provide a screenshot of window explorer with details (file name, extension visible, file size…) - A file transfer that have failed
- Hardware failure (SSD or HDD start to be tired…)
You can try to check your hard drive sanity, to verify if problem is not relative to a dead cell (SSD) or dead sector (HDD)
On my side, few month ago I loose hundred of files on a SSD drive: 10% cells dead and files stored on these cells were lost… 
Grum999