I’m not sure if I just don’t see it acting right, but I think I saw a couple of times where I would take a skull or cast the red brown bounty troup on an enemy, especially the legendary dragoness that has like 75% spell resist, and saw the stun disappear/resolve on my turn, making the spell do 20 damage instead of well over one hundred. Again, I might not have seen it resolve right, but I do believe there’s a bug with stun in this way. This event requiring so much stun brought it to light for me.
There might be additional boss traits at play, too — I don’t actually know if this is the case, though, because I haven’t bothered to check.
It was the weirdest thing. It only happened sometimes, presuming its coincidentally the turn the enemy would have cleansed the stun, but I’d cast on the Dragon legendary and her trait would go off even if she was stunned during my turn. I think the transition to their turn, since there’s no extra turn, means theres a 10, 20 30 etc percent chance each turn for them to have a sort of shadow cleanse simultaneously with your cast/skull take.