This occured on a somewhat old flash drive (HP C485L, 4 GB). The C485L has been reliable and never had data corruption so far, since at least 2014. But recently, something strange happened:
When I tried to mount it again, Linux spouted:
exited with non-zero exit status 32: mount: /dev/sdh: can't read superblock
Windows successfully mounted the drive, but no files are visible. The only thing is a new "System Volume Information" directory created shortly after insertion. However, the free space is around 1 GB, meaning that the FAT cluster map or whatever it is called, which marks clusters that are in use and tracks the fragmentation of files, must be intact.
Doing a quick scan with a prominent dutch data recovery program, the files recoverable through their header are undamaged, suggesting some kind of failed write.
What might have caused this strange error?
Could it be an unexpected disconnection? (I have always made sure to unmount/safely eject first.)