Bugged for me too. I've sat there for five minutes trying to move the key pillar back and forth dozens of times and cannot get it to slide over the cube lift. It gets caught and won't move past an invisible lip. Pushing, pulling, and sliding from the side don't make a difference. It is stuck and keeping me from finishing the tomb.

Same issue here. You take him down to zero health, perform the finishing animation and then he sits there for a second before ragdolling. Then if you hit him with an arrow or something he gets back up and starts swinging an invisible sword at you and is immune to all but arrow damage. I let him kill me three times and "finished" him 4 times with no success. This boss is straight trippin.