Ashe's ult = 0 damage no stun on hit? [all champions]

So it has happened a couple of times now and it is bugging me. Since 5.10 or around this. Most of the time the ult acts fine but, sometimes it just hits a champ and does nothing. No stun, no damage. really nothing. Just earlier in a SR match I shot my ult on a Fiddlestick, he never saw it coming and had started to recall, it hit straight on him and it only stopped his recalling. No stun, no damage... it was also shot from a considerable distance and the tip-target, as I'd call, was pointed right on fiddlestick when I fired the ult.

It happened twice or trice same match too, once. i think it even passed straight through an ennemy that had not used Zhonya or any other items one time. Has anyone experienced this problem too? I main Ashe, and this is really getting somewhat irritating XD