Ekko immune to stuns

I was playing a game as Annie, and i stunned both ekko and ahri at the same time, however ahri was stunned and ekko just blinked through my stun and kept going. Stun, knockup and fear are the only interrupts i know, so why doesnt ekko get affected by them? if this is the case im going to just keep banning ekko until they fix this bug.