Sheild bug

So i was playing and our zed was just about to be ulted by ziggs. like a good person i shielded him as the bomb came down but the shield didnt appear and zeds health didn't change noticeably. this is either some kind of shield invincibility glitch where the shield doesnt get put on(the explosion audio still played) or by pure coincidence my shield shield the exact amount of damage the the bomb did