Sivir Spell Shield Delay

Bump!

Can anyone explain this? Maybe I'm just lagging?

I just finished an ARAM where 50% or more of the time it wouldn't actually block anything.

Single spells right through. Combos, none of the spell affects blocked

I'd get the mana return, she'd say the emote. But the spell affect and the damage would go right through unhindered as if there was no spell shield.