Playing through the story mission 'In The Deep' and not sure if anyone else came across this, either since the reset or on their initial playthrough. Last part of the mission where you escape the hive, a yellow bar knight spawns along the way that you can damage and ultimately defeat if you hang around before going up the final set of stairs. I'm not sure if defeating the knight is what caused the buff 'Bane of the Catacombs' or if I just missed something earlier and it popped up then. At any rate, after some searching I found no one else describing this, so, yea, that's it. No idea what it did/does, but it lasted until reaching the top of the stairs and completing the mission.