I highly doubt you've lost multiple games due to this bug.
In order for this bug to effect gameplay, according to what you've said, you need:
To be playing Vel'Koz > To be in a game with an enemy using Warlord's Bloodlust > Enter combat with that one specific champion > Land your Q on them , which you could miss > Have them use the very short duration movement speed buff from Warlords RIGHT AS THEY GET SLOWED BY YOUR Q.
On top of that, you'd need to be in a position where it actually mattered. If you just hit them with your E or they aren't moving or someone else CC'd them, it doesn't matter.
I doubt the claim that on VERY RARE occurrences your Q did not slow the enemy, you lost the entire game. I cannot imagine this. Lets say this happened an unlikely amount of 5 times a game. And lets make another unlikely assumption in your favor, that every single one of these occurrences caused the enemy to either escape with their life or kill you. 5 potential kills or avoidable (if not for this bug) deaths are not going to completely lose you the game solely because of those. Especially if you already know of this bug and should have been able to avoid it, if it was really that bad.
You lost your games for reasons other than just the bug.