Ever since the update some spells refuse to launch. I heard this mentioned (ellyidol, I think) and it happened to me, too. Neither cooldown, vanilla nor global, was in effect at the time, but my drain life just wouldn't kick in no matter how I tapped it for a good while. This happened during a gnome king fight.

I can't say for sure, but it could also be that the normal cooldown animation got skipped for some reason. The effect would be the same.