I've recently come across another post with someone else experiencing this issue. But there have been multiple times that I have come across Kylo (Masked) and at the beginning of the battle my charact...
The 50% defense buff isn't supposed to stack, according to the information when reviewing the ability. But when the damage done to him dropped drastically was when he was by himself and he had a few DoTs on him. The characters I was using didn't apply any DoTs to him.