I suffered badly from this... currently waiting on an advisor for the second time to try and fix it.
Bottom line- this CAN happen. I played offline starting with about 6.75 hours of gameplay time. Over a week later, I booted up the game and I just happened to be connected to some local WiFi hotspot, so it asked if I wanted to sync my local files with the cloud- I assumes this meant that it would take all my current local non-cloud saves and ADD them to my cloud game saves, BUT NOPE! It overwrote my local non-cloud saves with my most recent ones. (Of which I had played approx 50 hours!)...
VERY annoying the way this cloud sync works. Under no circumstances should you be able to delete files on your computer with ONE CLICK. That is how accidents happen- accidents like mine.