[Gameplay] Amumu Q Not Reliably Hitting

Summoner's Rift Playing as Amumu, blue side (left side team).

Went in for gank in bot lane, from the river bush, Caitlyn was stunned by TF. Used my Q on Caitlyn while stunned; it missed completely.

Another instance, same game. Lux was stunned by TF in mid lane, used my Q on Lux, the animation went directly through her and it missed. Other Q's worked fine, but I have witness not understanding how it missed either.