So sometimes when I play as 
I dominate lol, but when i'm need some MR such as 
or 
her Q stops working. It wont activate it wont do anything. I tried binding and rebinding but still wouldn't work. And this only happens when I purchase these items. Hope im not the only one with this problem.
The Spectre Cowls weigh Vi down too much.
Interesting. I haven't heard of this one, but I'll give it a shot tomorrow to see if I can reproduce it.
I don't remember the items I had when it happened to me, but my Q stopped working after I fought with a Morgana. I was trying to double Q to interrupt her ult and from that point forward it refused to work. Rebinding, clicking, nothing. I had to kill the game with task manager and rejoin in order for it to work again, and by that time we were so behind it didn't matter since Vi is pretty worthless without her Q.
I had this issue one time. I asked in all chat and one of the enemy team said to hit alt q. After doing this it worked fine. Idk if the same thing but just thought I'd put this out there just in case.
While I do not remember if it happened after I bought a banshee veil, I remember that there was a ranked game where I could not use Q right after respawning and buying something. Only Q though, the rest were available to use.
I've had the same issue as well, it seems to happen specifically with spectres cowl.
Not sure if an update has been found on Riot's end, but it does seem to occur when you attempt to charge your Q at the moment you become CC'd. Two cases that have happened to me were Morgana ult and Jinx baby bear traps.
This bug also exists for Varus and his Q.
Killing the client and restarting seems to fix the bug.
A friend informed me that you can self cast the ability in order to use it, but I have not been able to personally test this.
This just happened to me in a Summoner's Rift game, at about the 30 minute mark I was unable to use Vi's Q. I had none of the items listed below.
