> later, when I tried to extract some large files from the backup, I saw that they had been replaced with some text files, containing a message that the download of those files failed.

That's a really asinine failure mechanism. At the very least, it should create "filename-FAILED_TO_RESTORE" or something like that.

Something that I was instructed to do nearly 30 years ago when at Motorola was: never overwrite the original files. Standard procedure was to make a directory called "BACKUP" (or "RESTORE"?) and put the files in there instead. The requesting person was then responsible for moving the files back to their original location, so any screwups were on them, not us (IT).