Thief Challenge - Life Stealer - Bugged and more

Hello,

After my friend decided to go for his mastery challenges I also wanted to go for them. I ran into an interesting bug for Thief while I did the "Life Stealer" challenge. Attached is the video of me doing it. https://youtu.be/Uyxny0X3liE 

Interestingly enough when I got back to the lobby not only was the challenge not done, but I had completed another challenge "Shattered Hopes". This is odd because earlier in the match I had grappled my way through a glass window but instead of defeating a runner I knifed a UESC bot.