Now Riven is Disabled

I'm not sure if this is the exact reason (it seems like it would be), but there was a bug with Riven that caused her to instantly recall by issuing a series of commands in very quick succession. Using it, I'd imagine Riven could escape nearly every gank.

if riven hit b in the middle of a combo she would insta-recall and immediately be in base.

her w+q combo caused her to instantly back if she pressed recall in the middle of it

Her animation cancelling reached a whole new level of bullshit. More in previous comments.

Zed infected her with something bad ;)

Instant recall bug.