I actually did use save to disk a couple times... a long while back. My last save to disk was just after I had first left Nogas, which was a long while ago. I stopped using it since the in-game save system appeared to work just fine and this is slower and less convenient, would have used it again if I closed the game down to pick up later.
Did not clear cache, or do anything different between this and my most recent save or load; saving had worked fine before, I had saved just before this (because, as I mentioned, I was expecting a high chance of game over), I had reloaded several times (also just recently, because I had game over'd from something else), not sure why everything suddenly disappeared without warning this time.
I would be completely fine if, instead of this happening, I had gone to save and found that everything had suddenly disappeared. Because then I'd just know to use save to disk all the time. But instead it all suddenly disappeared right when I most needed to load.
Just so we're clear, I'm not expecting to get my save back or anything; I fully understand that the data is gone. I just want whatever caused this in the first place to be fixed so this doesn't happen again, to me or anyone else.