Try a restart from your computer's power menu. (A restart, not a shut down.) And relaunch the game to see if your progress has returned. If it hasn't, it could be an Xbox Live outage.
Whenever Xbox Live goes down, progress disappears. We know that can be alarming but it comes back when the service is back up again.
To check the Xbox Live status, check out this article: How do I check the status of Xbox Live?
If the problem persists, please fill out a ticket here.