Mercenary not casting elemental weakness

Title. Mercenary does not cast ele weakness curse except maybe once a map. I have a sneaking suspicion it does not cast on enemies that are already cursed or have a mark.

Yeah I think thats the issue, its happening when you equip them with Asenath's as well. The temp chains curse makes her not cast ele weakness. I have her equipped with Deodre's ring as well. When i unequip asenath's she casts ele weakness.