This issue should be resolved with patch 0.3.0. If you continue to experience this issue, please reach out to us through our support site to let us know.
Some players are experiencing an issue where they are attempting to save the game while being in combat, jumping, or other activities where they aren't able to manually save, the game will fail to save the game and delete the previous save.
PC, Xbox One
Stand still outside of combat before manually saving your game.