This has been happening a lot more frequently to me and it doesn't just involve snares. However for me sometimes it seems random - I've had my Q interrupted many times before the second cast by a CC effect (stun, knockup, etc) but it will still work after - however when it does happen, it always seem to do so randomly (sometimes out of combat). However I have not been able to confirm/test it further. Most of the time when it happens it is during a teamfight, but there have been instances where it doesn't seem to be triggered by anything in particular.
To fix it in-game I put Q on smart cast, smart cast it, then take it off smart cast. It's worked every time the bug happened, but it's annoying to have to recall during a teamfight just to fix it.
Riot please look into this, I sent a support ticket to address the issue and saying there isn't a definite timeframe to fix it is kinda a cop-out. The same issue has been around for years, and it's one of the big known glitches (same with Varus and Warwick). It's pretty game-breaking, and I'm getting paranoid about playing her again. Vi's my main and I want to take her into ranked games, and I want to be sure I won't have to throw a match because of a glitch.
