File write failures causes loss of data.
open an existing file.
the file gets opened to be re-written
the HDD runs out of space
no data is written (cause you’re out of space)
file is left with size zero.
so now you have no where to write the file, and the file you did has all it’s content erased. congrats… you’ve now got the worst of all situations.
Why are files not transactionally written to disk?
Which version of N++ are you using? Could you please provide the debug info. Do you have one of the backup methods active (Settings->Options->Backup)?