Yasuo's third q (the tornado) will not work sometimes it shows that you have your q stacked than when you go to throw your third q he does the animation but the tornado does not show (also doesn't knock up any champions). This has happened plenty of times to me while trying to get away but i end up dying because they don't knocked up.
linkmastr0011 votesDid you let the stacks fall off? It doesn't stick around forever.
brookszombie3871 votesIt isn't often but i will try to throw it right away or even watch it go half way and than throw and it won't work
linkmastr0011 votesDo you have LoLreplay? If so, see if you can find a point (more then one preferably) where your q failed to be a whirlwind.
I'm not someone who works for Riot, but I am a developer. If you can find those points and put them into a video, I'm sure it would help Riot tremendously to identify the problem and fix it.
I don't play Yasuo often, but I've never seen the issue you're describing, and I know it can be tricky to describe how to reproduce bugs.