I play with two characters: A mage and a spellsword-style dude. About two weeks ago,I downloaded Dragonborn and Dawnguard.
I play with both characters. The spellsword, (L 52) started going to Solsthein, but I had trouble at one quest and a Black Book literally
disappeared, after a save, from my Inventory. I could not get it back and decided there was a glitch and sent him to start Dawnguard.
Completed through the 3rd main quest, Bloodline about three days ago. Played the Mage since.
Usually, I play with Steam off. But, go on Steam each week so the files can be "synched."
Today, I started to play--and was online with Steam--and noticed that my Spellsword character's saves (two) had been reverted to 2 weeks ago, even
though I had played just two days ago. A whole level was lost. I was back to 52, not at 53 and today I had to play several lead-ups to going to Dawnguard again.
ALL of my Dawnguard was gone.
Anyone else had probs like this?

You must disallow cloud syncing for your games in Steam (in Settings, tab "Download+Cloud"). You played off line during two weeks so, when you went back on line Steam compared your stored saves on their cloud with the ones you have in your computer. The system noticed that they were not the same and installed the saves they had instead of yours.

And Bethesda has nothing to do with this.