I can't seem to edit my above post, possibly because my account is new. It looks like this may be because there was some change today and the game started up with a "Crossplay Off" connection. I switched to Crossplay in the main menu, and then the save appeared in my list. We're actually both on Steam PC, but apparently it's still a Crossplay save. I don't know if there are still maintenance releases for the game, but if so in a situation like that the saves should probably be grayed out rather than missing.