There's something wrong with the stylish executioner, I found myself didn't go invisible after a stylish execution, if you watch the clip, the melee damage is still amplified, but no invisibility is granted after that. This invisible thing is like a gamble, sometimes it work (https://youtu.be/VydU-YokK_I), sometimes it doesn't. I also found out that this only applies to those who are one-shotted by the powered melee, if the melee doesn't kill it will be weakened.
Any help is much appreciated.
Stylish ex makes you go invisible when you kill an enemy under a weaken void effect. If you throw a grenade and weaken enemies, then kill one of them - you go invis. You can do the same with a smoke bomb. That's it. When you kill an enemy without any effect on it, you will not go invis. Your clip shows exactly that.