[Gameplay] Graves smokescreen and knockups

I ran and out graves's smokescreen as he was knocked up by my zyra ultimate and could not see him (or target him?) on my screen despite him appearing on my minimap so he should've been visible. He then reappeared at the end of the knockup, quickly zooming downwards from the top of my screen.

1. Zyra roots graves with e and knocks up graves.
2. Graves throws smokescreen on zyra
3. Zyra walks out of smokescreen as her ult's knockup triggers, graves can be seen on minimap as visible, but cannot be targeted as his model is not present.
4. The stun ends and graves's model reappears on my screen quickly zooming in from the top

giving your opponent 1 second of not being able to be targeted and stealth instead of a 1s knockup is a pretty big difference

My guess is that this is some sort of visual bug with knock-ups as you gain vision of a knocked up character and I may have been able to attack him with attack-move commands, but I figured he was in a bush until I looked at my map and then he reappeared near me and killed me.