Mordekaiser W Bug on minions [GAMEPLAY] #Gameplay

On Mordekaiser W on minions, the active part (recasting it)- doesn't always proc damage on all targets it's supposed to proc and it seems like it's random, but mostly I've noticed it bugs on "supposed-to-be" killing blows on minions. As you can see in the video the W active part procs on all the minions except for one melee creep. In this video of #SoloRenektonOnly (youtuber i took the clip from) this happened multiple times during his game. I myself have this bug over hundreds of times, every game, last 3 patches. Now it's getting frustrating especially since it seems like RNG. Sometimes it even misses the proc on 2 of 6 minions.