did you happen to close the computer down immediately after saving and exitting game?
sometimes if data is still writing from cache, it can be lost when shutting down pc before it finishes writing to disk. (it happens in background even if the game closes or the 'copy' window closes when moving files around in explorer etc).
it's possible with this particular game because of the many smaller files it writes.
this would be unusual, but something to rule out. if you are both on the public beta, even less likely to be what i say. and by 'immediately' above, i mean literally pushing the power button or clicking shutdown within moments of closing the ootp app. it would be a short window of time, and in some cases windows will delay shutting down until it finishes writing data, but this setting can be over-ridden by various apps or even by hand.
an app that 'speeds up computer' or anything akin to that (aka garbage app that does nothign but cause problems, lol) sometimes changes this registry key to speed up shutdown, for example, but any data being written is lost, including very important system-related things on occasion. never ever use an app that magically speeds up your pc... just buy a new pc
(just extra tidbit for fun, not an assumption)