Is stun bugged?

I am honestly not entirely sure whether this is an actual bug or simply an intended game mechanic. However, I am currently using the support gem Threshold with my auto attack in order to build up 99% of the stun bar and then finish off the boss with a single hit from the Bone Crusher skill.

This was working flawlessly until a few hours ago, but suddenly the mechanic started behaving as shown in the attached video. I can no longer execute my combo, and my build now feels broken in the worst possible way.

Could you please clarify if this behavior is intended?

How it should behave:

https://youtu.be/DQmQw4_zYS0

How it is behaving at the moment:

https://www.youtube.com/watch?v=Kd4vvj2KGpY

I think I’ve solved the puzzle… for some strange reason, this body armour I had equipped was causing the bug.

https://ibb.co/BVPFYhnZ