Vladimir Bug with his Q

Okay so basically I'm a Vladimir main and i play him a lot during ranked. And his Q sometimes goes off and sometimes it does not. For an example when I'm about to Q a dying minion or a cannon sometimes it doesn't go through until the last second. It goes through but it won't heal me afterward. I hate getting this because the casting is so delayed on Vladimir's Q. I tried this over and over in training and it still happens. This happens when the minion is really low at 1-2 hp. AND if you're thinking like what if it just died before I Q it? Well let me explain this, this only happens rarely but it happens of course. On my abilities when I Q something it sometimes says it goes through but I STILL have my red bar flowing my crimson rush attack. So clearly I did not get a healing from the dying minion but it says It went through. This happened so many times and I actually die a lot from this because it gives the enemy advantage to take me over because I don't have my Q charged up in time to counter. Even if i have W-pool ready for them I will not escape sometimes. This bug has been going on since the recent nerf on Vladimir. I am trying my best to use him the best of my use and Use him properly. I don't know if this a bug or a spell cast delay but this should probably get a fix so I can Q probably to minions and other champions. Like If i'm in range with my Q then it should go off right? Why is there a delay on Vladimir's Q. The animation is kind of weird sometimes. I get it he is pulling blood from something but it should at least be instant cause he is pulling blood instant. Thank you for reading this hopefully this gets fixed or an explanation.