Problems with Activated Abilities. Help

I have this problem with activated abilities stop auto attacking. Can someone tell me what I am doing wrong?

It happens to me with a lot of champions. But let me just give an example with VI. So her E makes her next auto attack empowered. There are times when I activate it and she just stands there.. It is as if I lose my Autoattack target, but my target is still alive. It is very frustrating, because i could have killed my target, but instead, I stop there, stand there like an idiot while my target gets away. It can't be me accidentally pushing Stop because I unbound the S key. Can someone tell me what I am doing wrong? or have an idea?

Another example is I would Q in to hit the target. Hit A to Auto attack the target. Hit E to auto attack cancel and empower next hit, but then she just stands there as if I pushed S to stop. It has made me lose team fights many times and miss kills many times.

I appreciate any help. or any theories of what is going on.

Cheers