OK, so I was doing some Vagary, when I noticed that all my gear save for weapons/ranged/ammo was locked in place (Encumbrance) during the fight against Plouton.
Your group needs to get better at fighting him and it will only be a minor issue. Whenever plouton gets nuked by the element he is currently strong against he will AoE Encumber everyone. The lengh of the encumbrace is directly proportional to the damage you healed.
So when he uses the "dustcloud 2hr" animation and changed weakness your group should only use very small nukes to probe it out. Then afterwards avoid the opposing element - that also includes magical WSes and skillchains.