I had a corrupted file and thought it was a corrupted file.
Later I downloaded another game and the dl stopped twice without notice, as if finished, but I noticed the file size was too small.
I tried using alternate download method and that seemed to work. All failed downloads came from the domain dl.itch.zone. The working download came from developername.itch.io.
It is quite unnerving that the download claimed to have finished instead of reporting an error.