Leg sweep sometimes does not stun

[Sinbios]

When it doesn't take, has stun been used on the same mob already?
What I mean is, stun may have diminishing returns. As in, works one time, maybe two, but not three, etc. on the same mob.

It has not, it was the first time I tried to use it on that mob. And if it has it will say the mob resisted it to some percentage.