Was doing Legend Seraph's Shield with a friend and we got soft locked due to the issue in the title. I think that the mission objective might not have changed to acquire the keycard iirc, but I may be wrong about that. Restarting the mission fixed it.
-
I kept running into this issue, I had to slow down in the start area. if you enter the elevator room before the enemies spawn in you bug out the level's checkpoints. once you kill the ogre and are going in try slowing down and walking. it worked for me. good luck!