i had the same shit happen, lost all my items in my stash (had 4 uniques for future alts, all my gems and crafting orbs). When I noticed that my items were missing, I re-started the game and poof, my character got re-rolled back to the start of act 2 (although I just did a mission in act 3 beforehand)
just be glad your character didnt get rolled back in the story :D

Me and my friend had the same probleme. We lost alot of items and he had to spend gold to unlock first stash tab 5 times before we logged off. This randomly happened from act1 to 3.

Got same problem, I put legendaries, gems etc. in stash a few minutes ago at town A2, then after changing to other char surprisingly all those things disappeared, no legends, no gems, no better flasks, strange... also interesting was that for a moment I've got twice unique swords 2H which i had only one before, how this mess happened to me.Looks that game is still offer bunch of shit, stopped blue screening every few minutes but now start messing up with items in stash. ..