Lightbringer bug ARAM [Gameplay]

In a recent ARAM game i played I decided to try out the Lightbringer item on Sivir. I was playing against a Fiora and right before she ulted I crit her. A couple ticks of her ult ticked and the animation played and then she just all of a sudden died in the middle of it. I can only assume that the cause of this was the item itself but it may be problem with Fiora, I am not for sure 100%.