Save overwritten by previous version

Whenever I click the play button on the main menu it does not load the most recent save. It only loads the most recent manual save, even if there's a more recent autosave.

This would be fine, if a little annoying, but as soon as the game loads it apparently immediately autosaves, so even if I quit without saving, my most recent autosave has been overwritten by the second most recent manual save and potentially a huge chunk of progress is lost.

Why does the game autosave as soon as it loads? Why does the play button autoload the most recent manual save rather than the MOST recent save regardless of whether it was manual or automatic? Is this just happening to me with my version or is this how the game works for everyone?

EDIT: I've been messing around and it doesn't seem to be happening anymore, but I don't know why it ever was or why it stopped so it could come back at any time. Maybe. I'd still appreciate any response.