Four times in a row, after dealing the final blow (of a bitch of a fight I might add), if you skip the victory cut scene it will insta-kill you and you will load outside the door to Lambach to start the fight over again. I thought maybe I was standing in a ground damage effect during the cut scene that was killing me, hence the 4 tries to figure it out. Finally let me complete it after making sure I wasn't standing in anything and not skipping the cut scene.

In the first phase of Lambach if you kill the spawn sack thingies on the rim of the room, often they do not regrow in future fights (unless you return to main menu and reload).

Same as above, last phase of the fight, the blood red ground damage effects will sometimes persist through your death to the next attempt. A few times it was more than just visual, the damaging effect persisted as well, where the entire floor was covered making the fight impossible. Other times even the green spotlighting effect persisted, mid-animation. Each of these could only be fixed by loading to main menu and fast traveling back to the fight.

When I encountered these bugs I was fighting Lambach on 1.0.3.0 with a Ranger dw pistol/turret build, on my second play through. My first play through on 1.0.3.0 I had no issues, using a Bladestorm/Juggernaut warrior character.