Diablo 3 coop overwrote single player game to older save

So long story short, I was near the last episodes(?) of ACT 2 when a friend invited me to a coop game. When I was done, I quit, went to the menu and hit resume and when I go in, it started me ALL the way back in ACT2 episode/chapter 1 when you first get to the city.

I go ahead and manually start the last episode I was on in act 2 but it literally took away all my last items, maps(uncovered/traveled to), equipped items etc..

I still have all my powers and slots that I set them to but essentially I’m going to have to redo all of the last missions I did before I joined that game.

My question is, is this a bug? Or something deliberate (which I highly doubt).
It upsets me because now I’m paranoid I’ll lose data when I join someone else’s missions.

Any one experience this or something I did wrong? I mean I always quit the same way so not sure whats going on.