Skarner's Impale (R) does not always cast (Gameplay)

I've had several occurrences where Skarner's Impale (R) fails activate and sometimes even stops Skarner in place. Without being CC'd in any kind of way and the enemy champion well within range it randomly does not work. I've had two instances where Skarner just stopped moving in the bush while trying to activate the R. I have even watched it effect Memento of Roccat against Splyce in Quarterfinals, Game 1 at 33:25, he flashes in the grab Caitlyn but it doesn't do (I attached a link to the game). I have been unable to replicate this on command but I know it happens. To me it happens maybe twice a game usually the ability as often as any other player would. Possibly too fast clicking lags it.