So apparently Vel'Koz can become invisible/untargetable/idk. Nobody could target him and he only showed up for a tiny blip if someone ran right up next to him. Pretty insane bug. Happened during the Onslaught difficulty on the NA server. Idk how to reproduce this as none of us had seen this bug happen before.
That vel'koz went into the fog of war, he wasn't untargetable. As for the bullshit that is how far a vel'koz can go on that particular wave, yes, that needs to be fixed
I'm pretty sure the poppy used her R on Vel and trowed him there, i did that stage A LOT of times and i'm pretty sure he spawn on the top side on the left side of the bridge ( at least there aren't some difference from EUW and NA ).
As for the bug itself i think he is just in the Fog of War like CaptainKemps noted.
