Originally posted by IceSkirmisher:

I had this exact same problem today. Logged in after building a fort for several days and suddenly everything was reset. Had any character, and could even look on my minimap and see where my bed was supposed to be. However everything else appeared to be reset. Would love to know if there is a fix, but I doubt it.

Yeah that is exactly what happened to me. I can still see my bed where my base was, but nothing there except for a fresh green forest now.