It's happening to me, with a sword also. The stunning is inconsistent...even getting the sound, then they've already teleported somewhere else.

I'm not trying to argue that the champions cant be dealt with with a sword (or by other means), I'm just saying that the overload mod isn't working as it should in regard to bows... or possibly in general, could be a latency issue, but even if that's the case that kind of thing should be handled client side