Version 1.5.3 rolled back to old save...lost 100+ hours

About 3 weeks ago, I loaded up my game with no problem.  Today, I loaded it up.  When I selected it, the save file size was above 20MB.  However, when the game loaded...it somehow rolled me back to a previous version from MONTHS ago and, easily, 100 hours of play lost.  When I exited the game, the save file is now only 6MB.  I am beyond frustrated with how much work I lost...

 

It's literally a previous save...not a corruption...so clearly you must keep versioned saves online somewhere...so hoping my world is not lost...