I’ve had this same issue. It’s happened to me twice. Both times when I pressed “Ctrl Z” to undo something. The first time I was able to get it back by rebooting, but not this time. All my backup folders just have .spj files, but the corrupt file is the .sll file, so that didn’t help.
I was able to get a backup by going to another branch in git, but I lost an hour’s worth of work.
It happened to me again. It seems to be related to using git. I’ve now lost another 2 hours of work. Any suggestions on how to recover the files? The backups aren’t helping.