I've had this happen to me for a couple games now and it is starting to get really annoying. When an entire piece of a champion's kit is gone, it will usually cripple them. I even died once and my Q still didn't work! I thought this bug was completely fixed by now and it's really freaking annoying me and probably every other person who plays Vi.
As a Vi main I feel your pain...
The workaround I've done whenever it happens is to put it on quickcast > quickcast it (there's gonna be a slight delay between when the command is given and when she actually performs her Q) > take it off quickcast. That works for me every time.
I've sent a ticket to Riot about it several months back and they have responded saying that there wouldn't be a specific timeframe for working on it, but they are looking into it. I think the problem stems from dying while charging your Q/getting your charge interrupted and immediately dying afterwards, but sometimes it happens at random and I'm not sure what causes it. If anything I think the fact that it's hard to reproduce is what's making it hard for Riot to fix.
Kind of related - her E isn't working as it should either (not all enemies in the cone are damaged, only the first few in front of her). I've heard they're fixing it in the new patch (along with all the other cone-related abilities) though.
It's been a problem for a long while and I hope Riot at least gets started on it - I've been wanting to take Vi into ranked for so long and now I can't climb using her..
