This sounds like what’s happening to me. I’ve finally found a pattern I can use as a workaround, which might also be a clue if it’s the same thing. If I run a security virus program scan, at first I thought I’d fixed it because it got rid of some viruses, but the pattern kept happening that it would not crash while the virus scan was running, but start happening when it was done. So it seems like something is going to sleep and triggering a shutdown, at least for me. And until my new laptop arrives, I’m going to be using running the virus scan as a workaround… it runs for two hours, I get two hours without a shutdown. But it’d be nice to figure out something more stable.