When fighting Dranos Velador, he is initiating a mechanic by jumping to each player and then locking down the player with taunt / he has aggroed.
Two adds need to be interrupted so the locked person can either block or dodge the next charged up attack.
Sadly atm this next charged up attack has no animation, so tanks die suddenly to no visible attack.
I recorded an two of those instances with Twitch on PC NA (I informed the other players).
Since I told the tank, he was waiting for the hit in block.
You can see Dranos being blocked and staggered backward, but his attack animation is not playing.
A similar bug was described in Oct. '16, but with prerequisites that I can not confirm. It happened everytime for us.
Here the video link.
(Dont mind the speaking, I was watching another stream on my second monitor)