I think they are fixing the bug in the shadow's attack once again. Before the patch, a Kensei Rin can trigger others in her aura to attack 3 consecutive times even when she only killed her primary target.Which mean it actually triggers up to the amount of attack a kensei Rin is capable of.
This may also be why a Ninja Shizu/Kai can reliably refresh on kill; it's because the aura actually stacked up to the amount of hit their normal attack can score.
it's been fixed now though. The aura works as intended (i.e: only triggers once if Rin killed one enemy)
Since they've fixed this 'problem' with the latest patch, I can only guess that's the reason why ninja's aura trigger rate is also affected.
Ahh makes sense! Come to think of it, he does look like he refresh more than once even if only one enemy is defeated before. Thought it was just the aura of another unit trigerring. Welp now i realize ill be remodelling my squad again for pvp. @.@