I have the same problem, but for me it's the shaman who always kills me. However, this has nothing to do with bad luck, because she always kills me out of nowhere with weak attacks, that normally take about 100 hp off me, but for some reason she instant kills me with that very same attack and takes me from full hp (1500) to zero. There's something wrong with the game.
I even scaled the difficulty all the way down to minimum and tried to freeze my hp with artmoney at 1500, which worked for every other fight against normal enemies in the same level, and I got killed by the shaman again the same way after three or four rounds.