First: Try to move them away from the door or any other obstacle.
Second: I don't see any sign of a debuff on Lucion but a couple seasons ago, when you have used banish on a boss, something like a streched HP bar happened, which would not adjust to the one you could see. As a result you wouldn't see some of the damage dealt up to a certain point but after that the decrease of the red bar happens faster per damage dealt than before. At least that is how I imagined it to be and it would just be a visual thing. I would recommend to just try to go on with the fight and see if still nothing happens with lucions health bar after a couple minutes.