There has been some instability with arcane spells since the new hak update. At times mass spells will not give effects to some in a party. Mass see invisibility, Mass improved invisibility, Mass bulls strength, Mass Haste, and Mass protection from elements, in this order failed to give their bonuses to one in our group who was in touching distance to the caster.
Also the Spell firebrand has been messed up for months. Some times nothing happens, no animation, no damage to enemies. other times it will only send out 1 or 2 brands, when it should send out as many as enemies present. (per it's description)