I used special of garnet on tier 2 which protects from ailments for 3 turns and next turn skadi of opponent fired. It killed minions by noor on my team and activated stack, 6% mana drop and frost damage.
It is because Skadi doesn’t give ailments, from which Garnet provides protection, but stacks. Those are stacks, a different thing, and Garnet can’t do anything about it.
For example, one of the heros that explicitly prevents stacks is Malosi: