I have this issue as well. I can save, but the moment I reboot or steam loses connection the saves all go bye-bye. This pretty much makes the game unplayable for me. So frustrating to get 20 days in and have a base setup all for it do disappear. Not only does it disappear, but I get no xp for the progress made. And before you ask, I have gone over the whole post and tried all the fixes, nothing saves my save-game when I do a reboot though.