I'll run a few tests and post the results in an hour or so. It is possible that that temporary copy is still there. I seem to remember that there were some threads not too long ago that talked about the game effectively working from a temporary copy of your save file somwehere in the ProgramData folder. With that out of the way, there may (just possibly) be a way to recover your save file. I have to agree with the others that it is not a good idea to shut down the computer when programs are still running.

Beyond frustrating I had gotten almost all the blueprints too and this is the only time this has ever happened Honestly this has burnt me out and I won't touch this for several months. I promise you, I saved that thing, MULTIPLE times, before turning my PC off. I do not understand, this is surely a bug of some kind, it really should not be happening in a complete game like this. But this one, this is the only one, from tonight, is the only one that is gone. ALL of my save files besides this one are still there - including files back from when I was playing this game back in 2017.

All of my progress, just vanished into thin air. I go to load subnautica a few minutes ago.and my file, is just, gone. I did not exit the game, just rebooted the whole PC. I save again, just to be sure, because I want to reboot my PC for a Windows update. I had gotten so far in this most recent playthrough, I just finished traversing the Degasi sea base with the crabsquid and Lost River, I had this super awesome base with all this stuff, I was getting ready to build Cyclops and find the last few alien bases, I saved my game like an hour ago.

Subnautica game not saving