There were two occasions where I had a draugr mob come out of a sarcophagus to attack me, and I wasn't able to hit it back. Its attacks landed on me like any other mob, but my attacks never landed, and it wasn't even affected by AOEs. In fact, I don't think the mob was even targetable, as if it were a background object that wasn't meant to come to life.
The first time, I was able to outrun it and it lost aggro. The second time, I couldn't get it off me and had to let it kill me so I could respawn and progress.
I'm going to submit it to ZOS as a bug, but was just curious if anyone else had run into this.