This is a known bug unfortunately and sorry to hear its happened to you.

In future please remember for Early Access especially i recommend backing up your game saves manually after each session. I do this and have managed to "side step" this bug on 2 occasions. There are tutorials on Youtube on how to do this.

Originally posted by cheachie:

THE GAME DID NOT BACK UO TO CLOUD

Do not rely on cloud, ever.
Even AAA games seem to have issues with Steam Cloud.