Karin (S) vs Karui (S)

It’s working fine for me.

Karin’s Raging Punch’s stun effect only works if the enemy’s health is at 15 or below.

Provide a screenshot next time so we can see the teams so we are able to do a further investigation about it for a better gameplay analysis. Otherwise we’re going to do nothing about it if it’s working fine on our part.

So you're telling me that Karin can only stun skills that stun, and not those skills that only have a secondary stun effect. She would stun Konan's Paper Shuriken for example, but would not stun Nagato's Ethereal Dragon?
Maybe it would be better to specify "Stuns skills that have a stun effect".